Disable RuboCop rake task for non-development environments like Heroku.
Merge pull request #10 from adaragroup/fix-heroku-rake-failure

Disable RuboCop rake task for non-development environments like Heroku.
Make the Playground Sinatra app have an actual name.
Move sprockets configuration into the Sinatra app.

Everything should be in one place!
rake assets now compiles our assets!
Document and obey Rubocop's instructions.