Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - fix tox error

    see logs

    https://build.opnfv.org/ci/job/dovetail-verify-master/560/console

    Change-Id: Ifa66087c4c8fcbaae809aae380587a4f03eded6c
    Signed-off-by: MatthewLi <matthew.lijun@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index faa79a9..56b5afa 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit faa79a9c2ffe8e1bd7ffef6e1b99ca30bd549641
+Subproject commit 56b5afa17e54e789715a5b22711e27a44a25168c