Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 855ebb920fc0a3ed29057178fbd602ee61716603
  - Chicken & egg in releng

    https://build.opnfv.org/ci/job/releng-release-v1.21-merge/4/console

    Change-Id: I9b7abcf0b5849646aad917fc072f52e122e89914
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 1f0a47d..855ebb9 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 1f0a47d255558da2432d1443790d2d544af2d2be
+Subproject commit 855ebb920fc0a3ed29057178fbd602ee61716603