gemspec: update killbill to 1.0.7

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
gemspec: update killbill to 1.0.8

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
travis: add ruby builds

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
Merge branch 'master' of github.com:killbill/killbill-logging-plugin