Update git submodules

* Update docs/submodules/apex from branch 'stable/fraser'
  - Pull stable branches of apex dependency repos instead of master

    Change-Id: Ie8178d2b99e7a977a7df697c6b39ee129c508107
    Signed-off-by: Feng Pan <fpan@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index e47c969..870c664 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit e47c969c9fd655b87670de13a4daac343a08f6db
+Subproject commit 870c66456c3e4d600a880df5b3612e5002fd9922