Regression fix: ensure .coffee is primary ext.

(The primary extension by default is the first extension, but the extensions
need to be in alphabetical order, and _coffee comes before coffee.)

lib/linguist/languages.yml

@@ -216,9 +216,9 @@ CoffeeScript:
   ace_mode: coffee
   aliases:
   - coffee
+  primary_extension: .coffee
   extensions:
   - ._coffee
-  - .coffee
   filenames:
   - Cakefile
 

test/test_language.rb

@@ -337,6 +337,8 @@ class TestLanguage < Test::Unit::TestCase
     assert_equal '.pl', Language['Perl'].primary_extension
     assert_equal '.py', Language['Python'].primary_extension
     assert_equal '.rb', Language['Ruby'].primary_extension
+    assert_equal '.js', Language['JavaScript'].primary_extension
+    assert_equal '.coffee', Language['CoffeeScript'].primary_extension
 
     # This is a nasty requirement, but theres some code in GitHub that
     # expects this. Really want to drop this.