Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Docker Builds from Git Tag"
  - Docker Builds from Git Tag

    Facilitates the creation of docker images from tags pushed to Gerrit,
    which should remove the need to manually trigger 'tagged' builds.

    Fixes a typo in the 'gerrit-trigger-tag-created' macro,
    replaces 'RELEASE_VERSION' with 'GERRIT_REFNAME', and adds the
    tag-trigger to docker builds.

    Change-Id: I6d8f8f34b1c51d74bb98211dfae21c37cf9356fa
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 4c51978..8a2c682 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 4c5197806b1ce162e19854975648528b1d10e2e2
+Subproject commit 8a2c682eb920ba5741577161ea23a678356da204