feat(plugins): normalize plugins and have unified function signature

src/lib/type.js

@@ -1,16 +1,18 @@
 const SemanticReleaseError = require('./error')
 
 module.exports = function (plugins, commits, lastRelease, cb) {
-  const type = plugins.analyze(commits)
+  plugins.analyze(commits, (err, type) => {
+    if (err) return cb(err)
 
-  if (!type) {
-    return cb(new SemanticReleaseError(
-      'There are no relevant changes, so no new version is released',
-      'ENOCHANGE'
-    ))
-  }
+    if (!type) {
+      return cb(new SemanticReleaseError(
+        'There are no relevant changes, so no new version is released',
+        'ENOCHANGE'
+      ))
+    }
 
-  if (!lastRelease.version) return cb(null, 'initial')
+    if (!lastRelease.version) return cb(null, 'initial')
 
-  cb(null, type)
+    cb(null, type)
+  })
 }