Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - More doc updates for Danube

    Change-Id: I125548acde034d8c4c85cce93fb001ba06c8ab33
    Signed-off-by: Tim Rozet <trozet@redhat.com>
    (cherry picked from commit 1d655538cfe9a665c5e12dc8b910ddaaae21bae7)

diff --git a/docs/submodules/apex b/docs/submodules/apex
index b4af8e1..55427ec 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit b4af8e13fd656423fe7275d6f37b7cfee10cd1aa
+Subproject commit 55427ec21a17cd601a4abb2cab4de4694ba1a702