Gazebo Version bump

6.0.0 -> 6.1.0
Fixing yosifkit's comment on docker-library/official-images#971

library/gazebo

@@ -10,7 +10,7 @@ libgazebo5:     git://github.com/osrf/docker_images@c7e0ac67d507b13e8b676a3d6480
 # 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
+gzserver6:      git://github.com/osrf/docker_images@892f4973b5016fc101ae7974be2a9571ea962dff gazebo/gazebo6/gzserver6
+libgazebo6:     git://github.com/osrf/docker_images@892f4973b5016fc101ae7974be2a9571ea962dff gazebo/gazebo6/libgazebo6
+latest:         git://github.com/osrf/docker_images@892f4973b5016fc101ae7974be2a9571ea962dff gazebo/gazebo6/libgazebo6
 # Docker EOL: 2016-01-25