message: CHANGE: Update Changelog
diff: * add 'gravity_vector' gravity ROS parameter to FrankaHWSim
  * Fix "Failed to create robot simulation interface loader" bug when installing from APT
  * Improve Gazebo 'stone' world objects
  +* Add `connected_to` option to `panda_gazebo.xacro` macro, similar to `panda_arm.xacro`
  ## 0.8.1 - 2021-09-08
  