Update git submodules

Update git submodules

* Update docs/submodules/apex from branch 'master'
  - Merge "Cleaning up yamllint warnings"
  - Cleaning up yamllint warnings

    apex/tests/config/inventory-virt-1-node.yaml
      1:1       warning  missing document start "---"  (document-start)

    apex/tests/config/inventory-virt.yaml
      1:1       warning  missing document start "---"  (document-start)

    build/opnfv-environment.yaml
      6:3       warning  comment not indented like content  (comments-indentation)

    Change-Id: Ice888464d09831066bb6cd0ac94fbd290b142088
    Signed-off-by: Dan Radez <dradez@redhat.com>