Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Change CentOS update repo location

    Change-Id: Id6e6297fe92271ba0a02057eeaf50b9a68edecf9
    Signed-off-by: Feng Pan <fpan@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 2f1c99d..44bafd3 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 2f1c99daeee9cf0e89a8e833e034e7a5979ae894
+Subproject commit 44bafd3a55c92920678687dbb3a9c015961649d6