Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "replace yaml.load with yaml.safe_load"
  - replace yaml.load with yaml.safe_load

    yaml.safe_load is safer, obviously.

    anteater will check for this

    template_format use specialized constructor based on yaml.SafeLoader

    JIRA: YARDSTICK-760

    Change-Id: Ia3b0b3aa0765385a0ee472a4d83f49d424b5a77f
    Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7786deb..4f13cac 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7786deb79662368c80386e6eaee4e9bfe12fcd2f
+Subproject commit 4f13caca517bd6ff31c0213ec7f9d8809dd4ef3c