Bump mutant version
Bump mutant version

Parser dependency has been updated in mutant itself.
Mutant gem releases are pushed to rubygems, no need to use custom ref
from github.

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