Upgrade to Ruby 2.1.4

@hsbt

Change version in Gemfile **and** .travis.yml to "2.1.4".

Using the "fuzzy matcher" `2.1` in .travis.yml (see c807ef2c1e9f16f195b152f42f2bbc6cd7feddb6) does not work at the moment, see @hone's PR (issue #869). Travis will use rvm with 2.1.3, and the build fails due to mismatch of the version specified in Gemfile and the actual Ruby version.