Add rake file to gemspec
Add rake file to gemspec

Fixes #69

Thanks @antage

jakeatwork/brakeman,masarakki/brakeman,spcoder/brakeman,masarakki/brakeman,bf4/brakeman,jakeatwork/brakeman,dfens/brakeman,spcoder/brakeman,bf4/brakeman,spcoder/brakeman,dfens/brakeman,bf4/brakeman,liqites/brakeman,oreoshake/brakeman,lee-leon/brakeman,cheerfulstoic/brakeman,oreoshake/brakeman,jeffyip/brakeman,lee-leon/brakeman,lee-leon/brakeman,htdc/brakeman,github/brakeman,jlecour/brakeman,codeclimate/brakeman-deprecated,jlecour/brakeman,jeffyip/brakeman,cheerfulstoic/brakeman,htdc/brakeman,kbrock/brakeman,github/brakeman,dfens/brakeman,cheerfulstoic/brakeman,jakeatwork/brakeman,jlecour/brakeman,liqites/brakeman,kbrock/brakeman,codeclimate/brakeman-deprecated,htdc/brakeman,liqites/brakeman,masarakki/brakeman,kbrock/brakeman