Update submodule mavlink v2.0 to latest Sun Aug 19 21:37:20 EDT 2018 (#10277)

- v2.0 in PX4/Firmware (485c5db2): https://github.com/mavlink/c_library_v2/commit/6404047979cadac62fecd75070cd995f1ca66ca2
    - v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/fe2349dea9a88fb5b873eff2a59a88125943fd61
    - Changes: https://github.com/mavlink/c_library_v2/compare/6404047979cadac62fecd75070cd995f1ca66ca2...fe2349dea9a88fb5b873eff2a59a88125943fd61

    fe2349d 2018-08-11 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/141637e21e87a9c4ade90dbb9d544375294c106a
1d49e43 2018-08-09 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/f4fda461caaa0cb2c5dfed20d21a9d2a254b6c03

v2.0 @ fe2349de

-Subproject commit 6404047979cadac62fecd75070cd995f1ca66ca2
+Subproject commit fe2349dea9a88fb5b873eff2a59a88125943fd61