Add Style/StringConcatenation to Rubocop config
Add Style/StringConcatenation to Rubocop config

This facilitates temporarily switching the mode of this cop.

MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer