Update submodule matrix to latest Wed Apr  8 12:39:43 UTC 2020
Update submodule matrix to latest Wed Apr  8 12:39:43 UTC 2020

    - matrix in PX4/Firmware (222e0636c4b53ea18013f2bf0d35a798fab6ae76): https://github.com/PX4/Matrix/commit/a32892926c69ea0bad031fd9d7bfc915cc5e9b68
    - matrix current upstream: https://github.com/PX4/Matrix/commit/d613055462bcbeacfd188cbd53de56c1dbc7b94d
    - Changes: https://github.com/PX4/Matrix/compare/a32892926c69ea0bad031fd9d7bfc915cc5e9b68...d613055462bcbeacfd188cbd53de56c1dbc7b94d

d613055 2020-04-06 kamilritz - Add more assignment operators for slices
976ada4 2020-03-21 Matthias Grob - Matrix: min max comments and test style
fa7153e 2020-03-21 Matthias Grob - Matrix: omit min max nan case with same result
PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,krbeverx/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware