Update submodule ecl to latest Mon Feb 3 12:39:22 UTC 2020

    - ecl in PX4/Firmware (5d62813): PX4/PX4-ECL@a3e1eb9
    - ecl current upstream: PX4/PX4-ECL@e52e2b8
    - Changes: PX4/PX4-ECL@a3e1eb9...e52e2b8

    e52e2b8 2020-02-01 kritz - Sensor Replay (#717)
da752c9 2020-01-28 kamilritz - Hot flow fusion fix
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