Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Update instack_undercloud yum update remove patch

    Change-Id: I0b812661c6217328c8b4efac4c69cb99d13418a8
    Signed-off-by: Feng Pan <fpan@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 4c1fa92..37fa680 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 4c1fa922f74113db7863bebcb833bdedbb4ad9d8
+Subproject commit 37fa680f248ac6f358b5a03ed431df3ef4aa958a