Fixes #3118 : upgrade Jgit to 2.2

linked to issue http://www.rudder-project.org/redmine/issues/3118

this upgrade is needed to resolve http://www.rudder-project.org/redmine/issues/3102

https://github.com/Normation/cf-clerk/pull/2 can also be accepted (upgrade to 2.1) as version 2.2 (out for 2 weeks when making the pull request)

maybe this one could be accepted later after upgrade to 2.1 had been accepted