Update submodule sitl_gazebo to latest Fri Jun 28 12:37:57 UTC 2019

    - sitl_gazebo in PX4/Firmware (7bba5a7): PX4/PX4-SITL_gazebo-classic@95adbb1
    - sitl_gazebo current upstream: PX4/PX4-SITL_gazebo-classic@22df947
    - Changes: PX4/PX4-SITL_gazebo-classic@95adbb1...22df947

    22df947 2019-06-27 Martina Rivizzigno - Range.proto: fix indentation
8ef5625 2019-05-28 Martina Rivizzigno - update sonar message to match mavlink distance sensor definition
e04ff96 2018-12-04 Martina - get distance sensor orientation from the vehicle model instead of hard-coding it in the gazebo interface, add horizontal and vertical fov