Build broken

When I updated Rails to the new version (Important: It fixes some XSS vulnerabilities), [the build broke](https://travis-ci.org/nerdhub/hcking/jobs/5619729). The reason for this is mocha. I locked it some time ago to a specific version, because updating it resulted in a broken build (API Changes) – and now the old version does not work with the current Rails. I don't have any experience with Mocha at all. @EinLama @bitboxer @klaustopher, you use it at work. Do you have experience with the update? If you don't, I'll bite the bullet and try to fix it (may only be a few minutes, but I don't know ;) ).