Update git submodules

* Update docs/submodules/releng from branch 'master'
  to a4d75e379dabd296ce021bea4e7f5d9f31f1f559
  - Fix tox.ini

    It leverages upper constraints and an updated jjb.

    Change-Id: I890acf8bf36a447e2fcd137cd1cd9e54d7cf5937
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 4978657..a4d75e3 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 49786579b6f81a6584eeede109e8aaadb83e8bbc
+Subproject commit a4d75e379dabd296ce021bea4e7f5d9f31f1f559