Specify ruby dev deps in Gemfile

.gitignore

@@ -2,6 +2,7 @@
 _gh_pages
 _site
 .ruby-version
+Gemfile.lock
 
 # Numerous always-ignore extensions
 *.diff

Gemfile

+source 'https://rubygems.org'
+
+group :development do
+  gem 'jekyll', '~> 2.5.2'
+  gem 'rouge', '~> 1.7.4'
+end