Update git submodules

Update git submodules

* Update docs/submodules/sfc from branch 'master'
  - Merge "Move the yamllint check to tox"
  - Move the yamllint check to tox

    Until now we were executing the yamllint check through shell
    commands contained to a builder in the releng repo [0].
    This patch moves that check to the tox framework.

    Additional changes should be done to the sfc jobs in the
    releng repo.

    [0]: https://github.com/opnfv/releng/blob/master/jjb/sfc/sfc-project-jobs.yaml#L73

    Change-Id: Ie42113087a8c1494593d5510cdf367abe99a7f5b
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>