Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 84a6d583428b452e64ab732043d6c455fab83cd6
  - Update to alpine 3.12 in jjbs

    https://alpinelinux.org/posts/Alpine-3.12.0-released.html

    Change-Id: I403aaae4168db8a22ad269daf1d6469ca73926a9
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 74f39df..84a6d58 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 74f39df873503b71c46aca2acf53a65b5003477f
+Subproject commit 84a6d583428b452e64ab732043d6c455fab83cd6