Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "update storperf installation in Yardstick"
  - update storperf installation in Yardstick

    Storper has updated its installaion step.
    The former used "nginx.conf" is not required any more.

    Change-Id: I9edd57ae7cffd3a95990844e6b775616d09132f1
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index f6a2413..3a87a32 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit f6a24134a515f419090bfd73663a9b1620964123
+Subproject commit 3a87a3262b5aefb7231f90a3b3808b947353eca5