Update submodule ecl to latest Tue Jan 28 12:39:24 UTC 2020

    - ecl in PX4/Firmware (a55547d): PX4/PX4-ECL@a3e1eb9
    - ecl current upstream: PX4/PX4-ECL@ee859e0
    - Changes: PX4/PX4-ECL@a3e1eb9...ee859e0

    ee859e0 2020-01-28 kritz - Robustify timestamp checks (#729)
f20726d 2020-01-23 kamilritz - Expand auto-format coverage and tiny style changes
fbdd75d 2020-01-27 kritz - Update CONTRIBUTING.md
5d38b73 2020-01-24 kamilritz - Update description of Firmware build tests
e3af91c 2020-01-24 bresch - Ekf: use helper functions to centralize the checks of horizontal aiding (gps, flow, ev_pos, ev_vel)

Author: PX4BuildBot