Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Add Promise gambia rtd job

    Change-Id: I122523925a022efe04040a021deebb257109132c
    Signed-off-by: Bertrand Souville <souville@docomolab-euro.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 10c59b4..4ff8abf 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 10c59b4c604637031f8bb601a824d8c4d2914fb3
+Subproject commit 4ff8abf9f2b32a28575b3c5f3dbf334f5a41c1de