Refactor to reuse built-in matcher.
Refactor to reuse built-in matcher.

At least shows difference when string not matched.

RailsEventStore/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,RailsEventStore/rails_event_store,mpraglowski/rails_event_store,arkency/rails_event_store,mpraglowski/rails_event_store,arkency/rails_event_store,RailsEventStore/rails_event_store