Fix Travis CI builds (the specs fail, due to clone --depth=50)

The specs depend on the `git log` by specifying a specific time range.
Travis CI will limit the git clone to a depth of 50 commits, thus this
causes some problems with our specs. An initial fix is to extend the
depth on Travis CI.
Remove version dependancies on charlock_holmes
Merge pull request #51 from kevinjalbert/fix-travis-builds

Fix Travis CI builds (the specs fail, due to clone --depth=50)