Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "[docs] Fix "Error in xxx directive" warning"
  - [docs] Fix "Error in xxx directive" warning

    JIRA: YARDSTICK-1416
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>
    Change-Id: I58c511454e052496e0b72ea28142b331514475c5

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 3418d76..189b829 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 3418d769a4bef9ea351e765fa00ad23986738e76
+Subproject commit 189b8296f83d9bb1fbbc5cf06d1f080f42b22cdf