Fix #92 properly- don't write malformed refspecs, but tolerate them

Use JGit library patched to tolerate the malformed refspecs generated by
JGit v1.0-v2.3.1 for bare-repo clones. From JGit v2.1 onwards (commit
3da13473), these malformed refspecs were no longer tolerated and would
stop fetches from updating refs. Normalising the refspecs fixes this
issue and allows fetches to update refs successfully.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=402031
Update to latest version of the scala-maven-plugin