Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Adding git as required dependency for Apex RPMs

      If it's not installed, opnfv-deploy will output an
      error message.

    JIRA: APEX-599

    Change-Id: Ib826204120f53abce1f4f1e3e4ec3119a71ab650
    Signed-off-by: Ricardo Noriega <rnoriega@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index dc55f3a..5255775 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit dc55f3a5bc343802bc60cd901ef8adcbafd3fe33
+Subproject commit 52557753e9cd240bc69d6b5d037a5b84e310050c