Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Remove arm build6 from rotation, it is offline

    Has been offline for > 1 week

    https://build.opnfv.org/ci/job/functest-core-docker-build-arm64-gambia/
    is showing
    There are no nodes with the label ‘Job triggered without a valid online
    node, given where: arm-build6’)

    Change-Id: Ia00281f9c05fac9b16bd914063ccffeca3fb135b
    Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index fc7b83b..aa9767d 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit fc7b83bbf7d52f8a952c2d923eaeb912e40af0f1
+Subproject commit aa9767d48171b6a3355bf1efd82a5f8afe7bbe2b