RFR- JL add email

users will receive emails when signing up for an account at OkBus, when they post a review, and when a review they authored is upvoted or downvoted.
Why don't you add back `ruby "2.0.0"`.  Later if we need to revert to 2.1 we can.  If we remove it entirely, we'll have trouble pushing our changes to Heroku.