Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add API(v2) to delete certain task"
  - Add API(v2) to delete certain task

    JIRA: YARDSTICK-738

    API: /api/v2/yardstick/tasks/<task_id>
    METHOD: DELETE

    Change-Id: I28215d2cae63551455abacc4142cff3c4aaed281
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 1cff540..134f174 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 1cff540d812ace29fa45bc789ad3a329435aa3ba
+Subproject commit 134f17488b8d0038999a1395c55992a41abae226