Update git submodules

* Update docs/submodules/dovetail from branch 'stable/fraser'
  - Update code base and docs to 2018.09

    The official name of the next release is going to be 2018.09.
    We need to rename all occurrences of 2018.08 in the code base,
    the documentation, and the web portal.

    JIRA: DOVETAIL-740

    Change-Id: Ie0e532d6671b7590454e9afd960a2934f313a022
    Signed-off-by: xudan <xudan16@huawei.com>
    (cherry picked from commit b65bbbc31c1a36e9981761712aea8ff17c8bc9de)

diff --git a/docs/submodules/dovetail b/docs/submodules/dovetail
index 74c2d0e..6ab9389 160000 (submodule)
--- a/docs/submodules/dovetail
+++ b/docs/submodules/dovetail
@@ -1 +1 @@
-Subproject commit 74c2d0e7beefe9a9804cc898634054097af851fa
+Subproject commit 6ab9389c04ce8b73e089b765c42722b25314d9e6