use github helper for dress_code gem in gemfile

Change-Id: I36af600183c33c47aac4547651db49362c52a91d
Reviewed-on: https://gerrit.instructure.com/40183
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Colleen Palmer <colleen@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

Author: ccutrer

Gemfile.d/assets.rb

@@ -1,5 +1,5 @@
 group :assets do
-  gem 'dress_code', '1.0.2', :git => "git://github.com/colleenpalmer/dress_code.git"
+  gem 'dress_code', '1.0.2', :github => "colleenpalmer/dress_code"
     gem 'colored', '1.2'
     gem 'mustache', '0.99.5'
     gem 'pygments.rb', '0.5.4'