Fix link to arel.

ugh.

Author: steveklabnik

Gemfile

@@ -11,7 +11,7 @@ if version == "master"
   gem "rails", github: "rails/rails"
 
   # ugh https://github.com/rails/rails/issues/16063#issuecomment-48090125
-  gem "arel", github: "arel/arel"
+  gem "arel", github: "rails/arel"
 else
   gem "rails", "~> #{version}.0"
 end