added rake development dependency, change http to https, add spec files to gem

Hello, 

we (Ruby Debian Group) would like to add your gem into Debian. While building your software, we are using unit / spec test to ensure, that our packages are working.

Your gem is missing the spec files from your repro. Could you please merge our pull request and release a new version on rubygems. So you can fetch the software from there, and do not need to patch your gem to distribute with Debian.

Thanks,

Jonas