Update doNotifyCommit for Jenkins ver. 1.580 and git plugin to 2.2.5

Gitorious plugin throws a NoSuchMethodError on "doNotifyCommit( String, String )" on Jenkins ver. 1.580 because the GitStatus class has been updated. This commit calls doNotifyCommit successfully with a null value.

Tested w/ Jenkins ver 1.58 and it successfully fires a build from Gitorious webhooks.