rubocop: configure the new Metrics/BlockLength cop
rubocop: configure the new Metrics/BlockLength cop

Fixes failing build.
The cop was introduced by:
https://github.com/bbatsov/rubocop/commit/96f308b4f5601f4642fadc5c5e2826d90df0c0f5

airbrake/airbrake-ruby,airbrake/airbrake-ruby