Bumping the crack version

[Security vulnerabilities have been discovered](https://support.cloud.engineyard.com/entries/22915701-january-14-2013-security-vulnerabilities-httparty-extlib-crack-nori-update-these-gems-immediately)
in <= 0.3.1 versions of crack. This change ensures that those versions
aren't used.
Merge pull request #247 from benilovj/patch-1

Bumping the crack version