Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Remove unused Docker build args

    Docker installed in OPNFV releng build servers doesn't allow unused
    args.

    Change-Id: I904d0542a8a9fd881ae66d65757a7b9bc8b74757
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 1cfa467..b599f27 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 1cfa467118efaf88d74aaa8b22b2daf247caa7c2
+Subproject commit b599f279ab63769b551d9a7802b297a870b7aba8