Update travis config file (PR #3400)

[arthurnn]

A few things in here:

• Test on ruby 2.2
• Allow failures in all variants of RAILS_MASTER test
• Use db:create task

review @SamSaffron @chancancode

GitHub

[discoursebot]

You’ve signed the CLA, arthurnn. Thank you! This pull request is ready for review.

[SamSaffron]

thanks!