Add `.rb` to the temp files passed to rubocop

Fixes #1652 and #1653. Rubocop is excluding files passed to it even if they are passed as command line parameters.

CHANGELOG.md

@@ -1,4 +1,5 @@
 # Next
+- Fix [#1652](https://github.com/Glavin001/atom-beautify/issues/1652) and [#1653](https://github.com/Glavin001/atom-beautify/issues/1653). Add `.rb` to temp files passed in to the `rubocop` executable so they are not excluded.
 - ...
 
 # v0.29.26 (2017-05-28)

src/beautifiers/rubocop.coffee

@@ -51,7 +51,7 @@ module.exports = class Rubocop extends Beautifier
         @run(rubocopPath, [
           "--auto-correct"
           "--config", configFile
-          tempFile = @tempFile("temp", text)
+          tempFile = @tempFile("temp", text, '.rb')
           ], {ignoreReturnCode: true})
           .then(=>
             @readFile(tempFile)
@@ -60,7 +60,7 @@ module.exports = class Rubocop extends Beautifier
         @run("rubocop", [
           "--auto-correct"
           "--config", configFile
-          tempFile = @tempFile("temp", text)
+          tempFile = @tempFile("temp", text, '.rb')
           ], {ignoreReturnCode: true})
           .then(=>
             @readFile(tempFile)