Use JGit 4.5.5
Use JGit 4.5.5

Includes security fixes which should be irrelevant to the Jenkins use
case.  Fixes are included just in case there is a surprise and they are
relevant to the Jenkins use case.

MarkEWaite/git-client-plugin,MarkEWaite/git-client-plugin,MarkEWaite/git-client-plugin