Bump babel-core from 4.0.2 to 5.1.11.

Notable new features from the [https://github.com/babel/babel/blob/master/CHANGELOG.md](changelog):
* Add [trailing function comma proposal](https://github.com/jeffmo/es-trailing-function-commas).
* Decorators based on [@wycat's stage 1 proposal](https://github.com/wycats).

There is a number of bug fixes and performance improvements, as well.

src/babel.coffee

@@ -28,10 +28,6 @@ defaultOptions =
     'useStrict'
   ]
 
-  # Includes support for es7 features listed at:
-  # http://babeljs.io/docs/usage/transformers/#es7-experimental-.
-  experimental: true
-
   optional: [
     # Target a version of the regenerator runtime that
     # supports yield so the transpiled code is cleaner/smaller.
@@ -43,6 +39,11 @@ defaultOptions =
     'reactCompat'
   ]
 
+  # Includes support for es7 features listed at:
+  # http://babeljs.io/docs/usage/experimental/.
+  stage: 0
+
+
 ###
 shasum - Hash with an update() method.
 value - Must be a value that could be returned by JSON.parse().