Let travis use its default bundler version.
Let travis use its default bundler version.

Rails 4.2.10 that we use for compatibility check requires bundler < 2.0
and by default travis has 1.16. Good enough for me.

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