Introduce Gerrit v3.7.8 and warn of not using 3.7.7

Add release notes of Gerrit v3.7.8 and discourage the use
of v3.7.7 due to the accidental revert of JGit to an earlier
SHA1.

Change-Id: Ic7fd755919e1b1fcac9d2ccc5bb8e90b9b09d331
1 file changed