Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "bug fix: bad path on auto generated documentation"
  - bug fix: bad path on auto generated documentation

    as mentioned in the jenkins logs [1], the folder is not correct
    replace functest/api/_
    build by docs/api/_build

    [1]: https://build.opnfv.org/ci/view/functest/job/functest-docs-upload-master/48/console

    Change-Id: I40f4c08474ff017f1616d463b6c5165cd6514c32
    Signed-off-by: Morgan Richomme <morgan.richomme@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index fc449f3..f21b646 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit fc449f385ce391f4cf0a35c098279e9d962a4320
+Subproject commit f21b646f8d2045179230c18a301b6e12699d4e80