fix cannot create hook without push_events bug

Because in GItlab, the push_events it default true in hooks: https://github.com/gitlabhq/gitlabhq/blob/master/db/schema.rb#L400

So, if you want to create hook only for merge_requests_events or issues_events, you must pass `push_events: true` in the arguments.

Now, the PR fix the bug ignore the argument.