Update submodule sitl_gazebo to latest Tue Feb 5 12:38:27 UTC 2019 (#11377)

    - sitl_gazebo in PX4/Firmware (6178ead6): https://github.com/PX4/sitl_gazebo/commit/12fb19ac6e7695ffc3dc9a64fcdd8499a522bd80
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/34d06e042c9dbd336899dbba373e32a6f19828b7
    - Changes: https://github.com/PX4/sitl_gazebo/compare/12fb19ac6e7695ffc3dc9a64fcdd8499a522bd80...34d06e042c9dbd336899dbba373e32a6f19828b7

34d06e0 2019-02-05 Tully Foote - create plane_cam world
93159f3 2019-02-01 TSC21 - CMakeLists: install package.xml
c5882f7 2019-01-31 Anthony Lamping - models: plane: split up, adding plane_cam
38fe49a 2019-02-01 TSC21 - Travis CI: do not pass user id env var to the container
0f1221b 2019-02-01 TSC21 - Travis CI: update Ubuntu container tags
bab0de9 2019-01-31 Anthony Lamping - models: remove matrice 100 opt flow meshes
0efbe69 2019-01-23 Oleg Kalachev - Fix building on macOS

sitl_gazebo @ 34d06e04

-Subproject commit 12fb19ac6e7695ffc3dc9a64fcdd8499a522bd80
+Subproject commit 34d06e042c9dbd336899dbba373e32a6f19828b7