Update git submodules

* Update docs/submodules/apex from branch 'stable/danube'
  - Pin puppet-fdio version for stable/danube

    Since stable/danube uses 17.04 release of VPP and Honeycomb,
    we need to pin puppet-fdio to the commit before 17.07 specific
    interface role tagging changes.

    Change-Id: Id2c52679ab5bc74995149ed1df5365b934f89c3f
    Signed-off-by: Feng Pan <fpan@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index 341d03f..ec255e7 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit 341d03f86b718e0d556c2e12baebdca8760a28ec
+Subproject commit ec255e70792340c86d5e1a975ac1ae94b135fb8e