Update git submodules

* Update docs/submodules/promise from branch 'master'
  - Update Config Guide

    Change-Id: Ibac4f47889ec0d0349d29eaffb61bcf070d99eb3
    Signed-off-by: Bertrand Souville <souville@docomolab-euro.com>

diff --git a/docs/submodules/promise b/docs/submodules/promise
index 30125bc..b121b21 160000 (submodule)
--- a/docs/submodules/promise
+++ b/docs/submodules/promise
@@ -1 +1 @@
-Subproject commit 30125bcaa029df296a2dd2b214774e36ec995a24
+Subproject commit b121b21df581291cd273a9a8acc1d4f266116022