Issue 4000: Upgrade protobuf-gradle-plugin (#4001)
Issue 4000: Upgrade protobuf-gradle-plugin (#4001)

Upgrades protobuf-gradle-plugin to 0.8.9

Signed-off-by: Flavio Junqueira (fpj) <48c356ff4855e878e2050cfad72b47f4633a5eef@emc.com>
pravega/pravega,pravega/pravega,pravega/pravega