Merge pull request #20 from mbj/master

Upgrade backports gem dependency
Bump version to 0.0.8

It should be our policy to bump versions just after each release to
rubygems.org.

My idea is the following:

If I need stuff that is only in the git source, I can set a version
requirement that is unsatisfiable by rubygems. If I forget to include
the git source in Gemfile I'll immediately notice this, because I cannot
bundle anymore.