Fix instrumentation include for Sintra

The `NewRelic::Agent::Instrumentation::ControllerInstrumentation` module does an `extend` on the `included` hook. At present, it is extending onto the `NewRelic::Agent::Instrumentation::Sinatra` module, but those class methods should be added to the `::Sinatra::Base` class.

This fixes that issue by moving the include of the `ControllerInstrumentation` into the `Sinatra::Base.class_eval` block.