Adding v6.0 and tagging libgazebo6 as latest

library/gazebo

@@ -1,6 +1,11 @@
 # maintainer: Nate Koenig <[email protected]> (@nkoenig)
 
 gzserver5:      git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo5/gzserver5
-latest:         git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo5/gzserver5
+libgazebo5:     git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo5/libgazebo5
 # Docker EOL: 2019-04-30
 # LTS
+
+gzserver6:      git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo6/gzserver6
+libgazebo6:     git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo6/libgazebo6
+latest:         git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d648051997a871f6b gazebo/gazebo6/libgazebo6
+# Docker EOL: 2016-01-25