Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "[yardstick] fraser opnfv-6.1.0 release tag"
  - [yardstick] fraser opnfv-6.1.0 release tag

    Change-Id: Ife8ee87db45381678c44ebd80adf08658bd697f5
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index ac20f94..18ebc30 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit ac20f94f10934a3f6909e860bfc5ac19749dcc1e
+Subproject commit 18ebc30af6c2da4cbede2c997619fe6bfdb8cfed