Fixed a NameError (uninitialized constant) problem

When I use this gem with Rails 3.2.13 and run `rails console`, this gem raises the following error.
* ruby/2.0.0/gems/newrelic-grape-1.2.0/lib/newrelic-grape/instrument.rb:5:in `<class:Grape>': uninitialized constant NewRelic::Agent::Instrumentation::Grape::ControllerInstrumentation (NameError)