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

.travis.yml

@@ -6,10 +6,9 @@ cache:
 notifications:
   email: false
 node_js:
-- v5
-- v4
-- iojs-v2
-- iojs-v1
+- 5
+- 4
+- iojs
 - '0.12'
 - '0.10'
 before_install:
@@ -19,3 +18,5 @@ before_script:
 after_success:
 - npm run coverage:upload
 - npm run semantic-release
+services:
+- couchdb