Upgrade `rugged`, Bump Version Number.

This PR upgrades `rugged` to version 0.21.0 and bumps the gem version to 2.2.2. It also addresses two deprecation warnings found when running `rspec`, and makes the following changes to the Travis CI environment:

   * Travis runs CI on Ruby 2.1.2 instead of 2.0.0.
   * Travis updates its `git` config to see all remote branches, instead of just the branch Travis pulled from. This fixes an issue in which some tests that pass locally fail in CI.