Update git submodules

* Update docs/submodules/dovetail from branch 'master'
  - Bugfix: build docker image failed

    1. When build Dovetail docker image, the job failed.
    2. https://build.opnfv.org/ci/view/dovetail/job/dovetail-docker-build-push-master/279/console
    3. That's because the setuptools version is old.
    4. It needs to upgrade setuptools in the Dockerfile.

    JIRA: DOVETAIL-534

    Change-Id: If37a4d7c3b57ea79903565fd880c5447da97b13b
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 4e37ee1..7825761 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 4e37ee139ef18890dcfd42bea84974ea10535793
+Subproject commit 78257613e55d1af14a5ce73f32859de0c9054bbf