Rename `BeforeHook#before` to `before_rake_task` to avoid conflict

If you have `sinatra` and `sinatra-assetpack` in your Gemfile together with `bower-rails`, it will conflict with this method name `before`, causing bower-rails hook tasks to not run at all.

If you try to setup a brand new Rails app with the `sidekiq-benchmark` (0.4.1 at the moment), you will be able to reproduce this bug.