Added Rakefile

This is needed for our continuous integration.

Bug: T117993
Change-Id: Ibb17cdd346f72af767d2c46319737438e489520a

Rakefile

@@ -0,0 +1,14 @@
+require 'bundler/setup'
+
+require 'rubocop/rake_task'
+RuboCop::RakeTask.new(:rubocop) do |task|
+  # if you use mediawiki-vagrant, rubocop will by default use it's .rubocop.yml
+  # the next line makes it explicit that you want .rubocop.yml from the directory
+  # where `bundle exec rake` is executed
+  task.options = ['-c', '.rubocop.yml']
+end
+
+task default: [:test]
+
+desc 'Run all build/tests commands (CI entry point)'
+task test: [:rubocop]