Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Updates release notes for Danube

    Change-Id: Id3a90d1ba53502bc28db3e04d2795e9806f42eed
    Signed-off-by: Tim Rozet <trozet@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index a684f6b..9881eac 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit a684f6b753749c355aee06412bd0f22779357089
+Subproject commit 9881eac1a9b1cc32ba7239e3d9189df3c11784ac