Fix issue #707 by adding Atom-based EOL detection

Determines the default line ending based upon the Atom configuration
`line-ending-selector.defaultLineEnding`. If the Atom configuration
indicates "OS Default", the `process.platform` is queried, returning
CRLF for Windows systems and LF for all other systems.

src/beautifiers/js-beautify.coffee

@@ -24,6 +24,9 @@ module.exports = class JSBeautify extends Beautifier
   beautify: (text, language, options) ->
     @verbose("JS Beautify language #{language}")
     @info("JS Beautify Options: #{JSON.stringify(options, null, 4)}")
+    #TODO reconsider handling of EOL once js-beautify adds EOL detection
+    #see https://github.com/beautify-web/js-beautify/issues/899
+    options.eol = getDefaultLineEnding() ? options.eol #fixes issue #707
     return new @Promise((resolve, reject) =>
       try
         switch language
@@ -52,3 +55,23 @@ module.exports = class JSBeautify extends Beautifier
         reject(err)
 
     )
+
+  # Retrieves the default line ending based upon the Atom configuration
+  #  `line-ending-selector.defaultLineEnding`. If the Atom configuration
+  #  indicates "OS Default", the `process.platform` is queried, returning
+  #  CRLF for Windows systems and LF for all other systems.
+  # Code modified from atom/line-ending-selector
+  # returns: The correct line-ending character sequence based upon the Atom
+  #  configuration, or `null` if the Atom line ending configuration was not
+  #  recognized.
+  # see: https://github.com/atom/line-ending-selector/blob/master/lib/main.js
+  getDefaultLineEnding= ->
+    switch atom.config.get('line-ending-selector.defaultLineEnding')
+      when 'LF'
+        return '\n'
+      when 'CRLF'
+        return '\r\n'
+      when 'OS Default'
+        return if process.platform is 'win32' then '\r\n' else '\n'
+      else
+        return null