Update git submodules

* Update kubernetes/robot from branch 'frankfurt'
  to 878f64c190e1dc5937ed30ff13921ff7fb1cbd97
  - Bump 1.6.4 version for Frankfurt maintenance release

    This new version includes minor fixes for ue case support

    Issue-ID: INT-1652

    Signed-off-by: mrichomme <morgan.richomme@orange.com>
    Change-Id: I773d78906c5b32678e58eafe825ba12059ff52cf
    (cherry picked from commit 44a38a594677ca38c4eea288908ebf503ad91b4e)

diff --git a/kubernetes/robot b/kubernetes/robot
index 36eee93..878f64c 160000 (submodule)
--- a/kubernetes/robot
+++ b/kubernetes/robot
@@ -1 +1 @@
-Subproject commit 36eee9317915ad1728421a5abeaa84fff239911c
+Subproject commit 878f64c190e1dc5937ed30ff13921ff7fb1cbd97