Update submodule sitl_gazebo to latest Wed Nov 21 00:37:52 UTC 2018

    - sitl_gazebo in PX4/Firmware (560a9b45): https://github.com/PX4/sitl_gazebo/commit/3d80f63562c24c1537e1f8423ce649c99ebc15ea
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/2adc86b5bf84543091470966caf33c3b4f3ee666
    - Changes: https://github.com/PX4/sitl_gazebo/compare/3d80f63562c24c1537e1f8423ce649c99ebc15ea...2adc86b5bf84543091470966caf33c3b4f3ee666

    2adc86b 2018-11-14 Elia Tarasov - add max value for wind and wind gust means
fb20a36 2018-11-14 Elia Tarasov - add normal gaussian distribution to wind gust force and direction
bd5ce12 2018-11-14 Elia Tarasov - add normal gaussian distribution to wind force and direction
913c094 2018-11-07 Jacob Schloss - reverse order of test
7d08ef5 2018-11-07 Jacob Schloss - fall back to only enabling up to c++14 on old cmake
0fd93b0 2018-11-07 Jacob Schloss - set CMAKE_CXX_STANDARD so cmake does not append a defualt language standard