Merge branch 'stable-2.16'

* stable-2.16:
  Upgrade guava to 26.0-jre
  Upgrade JGit to 5.1.5.201812261915-r
  Upgrade JGit to 4.9.8.201812241815-r
  Upgrade JGit to 4.7.7.201812240805-r

Change-Id: Ib2e16d7ec9459147d9e961ad3d9e6e3707a027c9