Update git submodules

* Update docs/submodules/releng from branch 'master'
  to ca06ec4619461ac53ad3e8b783a160bfed95c273
  - Rewrite generate-artifacts-index-pages

    lf-build6 is offline.

    Change-Id: I0c0b8b9e3a7dcb00a0ac6cac4883e32c8315373d
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index e0cd977..ca06ec4 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit e0cd9779935689926cb3c9ff0575c9143dda0767
+Subproject commit ca06ec4619461ac53ad3e8b783a160bfed95c273