Update submodule matrix to latest Sun Sep 22 08:37:30 EDT 2019

    - matrix in PX4/Firmware (8b1f954): PX4/PX4-Matrix@60c9c99
    - matrix current upstream: PX4/PX4-Matrix@c34e8dc
    - Changes: PX4/PX4-Matrix@60c9c99...c34e8dc

    c34e8dc 2019-09-17 Matthias Grob - helper: consider matrices with the same NANs and INFINITYs equal
bbaa938 2019-09-17 Matthias Grob - helper: consider NAN equal to NAN such that vectors can be compared exactly
33a6291 2019-09-17 Matthias Grob - Matrix: add proper print function testing
b0b7d72 2019-09-17 Matthias Grob - Multiplication test: fix division resulting in NAN
3747232 2019-09-17 Matthias Grob - LeastSquaresSolver: Fix nasty GCC compile optimization error
5844b0e 2019-09-16 Matthias Grob - Implement one float equality check and use it everywhere
1e80807 2019-09-16 Matthias Grob - test: Add uncovered equality checks with NAN and INFINITE
a374f37 2019-09-16 Matthias Grob - Include helper_functions like all other library components