Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Fix Manual Triggering of Docker Jobs

    When manually triggering a docker job (or even through timed builds),
    GERRIT_EVENT_TYPE will not get set. This does gets set when the job is
    triggered by a Gerrit event (ex: ref-updated, comment-added).

    Specifying the variable lookup to default to nothing (ex: "${FOO:-}")
    should allow non-Gerrit triggered jobs to complete successfully.

    Change-Id: Ic1ba8ebef0967b0f20a2d6385ce0e0b4876901dc
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>