Ensure that all source files end with a single \n

[lydell]

This was done by first checking all files in the repository root by hand, and
then by doing the following:

$ npm i get-stdin@4
$ cat clean.coffee
fs = require 'fs'
stdin = require 'get-stdin'

stdin (text) ->
  for file in text.trim().split('\n')
    contents = fs.readFileSync file
      .toString().replace /\s*$/, '\n'
    fs.writeFileSync file, contents
  return
$ ls !(node_modules)/**/*.coffee | coffee clean.coffee

Ideally merged after #4079.

[michaelficarra]

Thanks.