Update submodule sitl_gazebo to latest Sat Aug 8 00:38:33 UTC 2020

    - sitl_gazebo in PX4/Firmware (3002e74): PX4/PX4-SITL_gazebo-classic@037ce1b
    - sitl_gazebo current upstream: PX4/PX4-SITL_gazebo-classic@0da08f0
    - Changes: PX4/PX4-SITL_gazebo-classic@037ce1b...0da08f0

    0da08f0 2020-08-07 SungTae Moon - Add iris_rtps model (#558)
6e5e882 2020-08-05 Ali Tlisov - fixed spanwise velocity component calculation (#562)
5a19094 2020-08-05 JaeyoungLim - Lower wind topic publish rates to 2Hz to increase realtime factor (#561)
0756bcf 2020-08-04 Julian Oes - standard_vtol: make hover motors stronger
2858552 2020-08-04 JaeyoungLim - Fix airspeed sensor wind subscription
89755a1 2020-07-23 JaeyoungLim - Fix wind topic names for vtols