Upgrade JGit to 4.9.7.201810191756-r

It contains fix for 'LFS: file handle leak in ObjectDownloadListener'
issue [1].

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=540049

Change-Id: Idc462272f7ab8dae8bd52e8e599d65223b9c0083
1 file changed