[TASK] Move Brakeman out of the Gemfile.

Brakeman has some very special dependencies which conflict with the other
Gems which we're using.

This change moves Brakeman out of the Gemfile and into manual installation
via the Travis configuration.

Resolves: GET-7
Merge pull request #48 from braingourmets/task/brakeman

[TASK] Move Brakeman out of the Gemfile.