Migrate from FEST 2 to AssertJ

The migation guide at http://joel-costigliola.github.io/assertj/assertj-core-migrating-from-fest.html described all necessary steps to migrate from FEST 2.x to AssertJ 1.6.0.

In the future [assertj-joda-time](http://joel-costigliola.github.io/assertj/assertj-joda-time.html) and [assertj-guava](http://joel-costigliola.github.io/assertj/assertj-guava.html) might also come in handy for writing more concise tests for Dropwizard (which is using both, JodaTime and Google Guava).
Thanks for spotting this! I simply forgot to change the version in `dropwizard-testing` as well.