chore: remove babel, fix integration tests

This commit removes babel/es6 from all source and test files, because it was introducing a lot of overhead and only little gain.
This commit fixes and enables integration tests on Travis.
This commit fixes #153 and #151 along the way.

_Originally this commit should have only removed babel, but without working tests that's a bit too hairy._
_I only realized that half way into removing babel/es6, so things are all over the place now._

Closes #153, Closes #151

src/lib/commits.js

@@ -1,39 +1,43 @@
-const { exec } = require('child_process')
+var exec = require('child_process').exec
 
-const log = require('npmlog')
+var log = require('npmlog')
 
-const SemanticReleaseError = require('@semantic-release/error')
+var SemanticReleaseError = require('@semantic-release/error')
 
-module.exports = function ({lastRelease, options}, cb) {
-  const branch = options.branch
-  const from = lastRelease.gitHead
-  const range = (from ? from + '..' : '') + 'HEAD'
+module.exports = function (config, cb) {
+  var lastRelease = config.lastRelease
+  var options = config.options
+  var branch = options.branch
+  var from = lastRelease.gitHead
+  var range = (from ? from + '..' : '') + 'HEAD'
 
   if (!from) return extract()
 
-  exec(`git branch --contains ${from}`, (err, stdout) => {
-    let inHistory = false
-    let branches
+  exec('git branch --contains ' + from, function (err, stdout) {
+    var inHistory = false
+    var branches
 
     if (!err && stdout) {
       branches = stdout.split('\n')
-      .map((result) => {
+      .map(function (result) {
         if (branch === result.replace('*', '').trim()) {
           inHistory = true
           return null
         }
         return result.trim()
       })
-      .filter(branch => !!branch)
+      .filter(function (branch) {
+        return !!branch
+      })
     }
 
     if (!inHistory) {
       log.error('commits',
-`The commit the last release of this package was derived from is not in the direct history of the "${branch}" branch.
-This means semantic-release can not extract the commits between now and then.
-This is usually caused by force pushing, releasing from an unrelated branch, or using an already existing package name.
-You can recover from this error by publishing manually or restoring the commit "${from}".` + (branches && branches.length
-        ? `\nHere is a list of branches that still contain the commit in question: \n * ${branches.join('\n * ')}`
+        'The commit the last release of this package was derived from is not in the direct history of the "' + branch + '" branch.\n' +
+        'This means semantic-release can not extract the commits between now and then.\n' +
+        'This is usually caused by force pushing, releasing from an unrelated branch, or using an already existing package name.\n' +
+        'You can recover from this error by publishing manually or restoring the commit "' + from + '".' + (branches && branches.length
+        ? '\nHere is a list of branches that still contain the commit in question: \n * ' + branches.join('\n * ')
         : ''
       ))
       return cb(new SemanticReleaseError('Commit not in history', 'ENOTINHISTORY'))
@@ -44,16 +48,18 @@ You can recover from this error by publishing manually or restoring the commit "
 
   function extract () {
     exec(
-      `git log -E --format=%H==SPLIT==%B==END== ${range}`,
-      (err, stdout) => {
+      'git log -E --format=%H==SPLIT==%B==END== ' + range,
+      function (err, stdout) {
         if (err) return cb(err)
 
         cb(null, String(stdout).split('==END==\n')
 
-        .filter((raw) => !!raw.trim())
+        .filter(function (raw) {
+          return !!raw.trim()
+        })
 
-        .map((raw) => {
-          const data = raw.split('==SPLIT==')
+        .map(function (raw) {
+          var data = raw.split('==SPLIT==')
           return {
             hash: data[0],
             message: data[1]

src/lib/get-registry.js

@@ -3,8 +3,8 @@ module.exports = function (pkg, conf) {
 
   if (pkg.name[0] !== '@') return conf.get('registry') || 'https://registry.npmjs.org/'
 
-  const scope = pkg.name.split('/')[0]
-  const scopedRegistry = conf.get(`${scope}/registry`)
+  var scope = pkg.name.split('/')[0]
+  var scopedRegistry = conf.get(scope + '/registry')
 
   if (scopedRegistry) return scopedRegistry
 

src/lib/plugins.js

@@ -1,14 +1,14 @@
-const relative = require('require-relative')
-const series = require('run-series')
+var relative = require('require-relative')
+var series = require('run-series')
 
-let exports = module.exports = function (options) {
+var exports = module.exports = function (options) {
   var plugins = {
     analyzeCommits: exports.normalize(options.analyzeCommits, '@semantic-release/commit-analyzer'),
     generateNotes: exports.normalize(options.generateNotes, '@semantic-release/release-notes-generator'),
     getLastRelease: exports.normalize(options.getLastRelease, '@semantic-release/last-release-npm')
   }
 
-  ;['verifyConditions', 'verifyRelease'].forEach((plugin) => {
+  ;['verifyConditions', 'verifyRelease'].forEach(function (plugin) {
     if (!Array.isArray(options[plugin])) {
       plugins[plugin] = exports.normalize(
         options[plugin],
@@ -20,7 +20,7 @@ let exports = module.exports = function (options) {
     }
 
     plugins[plugin] = function (pluginOptions, cb) {
-      var tasks = options[plugin].map((step) => {
+      var tasks = options[plugin].map(function (step) {
         return exports.normalize(step, './plugin-noop').bind(null, pluginOptions)
       })
 

src/lib/type.js

@@ -1,9 +1,10 @@
-const SemanticReleaseError = require('@semantic-release/error')
+var SemanticReleaseError = require('@semantic-release/error')
 
 module.exports = function (config, cb) {
-  const { plugins, lastRelease } = config
+  var plugins = config.plugins
+  var lastRelease = config.lastRelease
 
-  plugins.analyzeCommits(config, (err, type) => {
+  plugins.analyzeCommits(config, function (err, type) {
     if (err) return cb(err)
 
     if (!type) {

src/lib/verify.js

@@ -1,9 +1,12 @@
-const parseSlug = require('parse-github-repo-url')
+var parseSlug = require('parse-github-repo-url')
 
-const SemanticReleaseError = require('@semantic-release/error')
+var SemanticReleaseError = require('@semantic-release/error')
 
-module.exports = function ({pkg, options, env}) {
-  let errors = []
+module.exports = function (config) {
+  var pkg = config.pkg
+  var options = config.options
+  var env = config.env
+  var errors = []
 
   if (!pkg.name) {
     errors.push(new SemanticReleaseError(