Pin dependency to last-known-working version.
Pin dependency to last-known-working version.

[Closes #449]

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