Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Removing trailing whitespace

    Change-Id: I0380deec3e41a6dc02571ed9c4fa16e304f7f85e
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 1ca9d52..255d5a5 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 1ca9d52152d54b51b4d9dcd6c429f114ad4fe24c
+Subproject commit 255d5a579ce0ce4acabd971b94f36fe288fe7489