Update git submodules

* Update docs/submodules/snaps from branch 'master'
  - Merge "Apply upper-constraints when testing SNAPS"
  - Apply upper-constraints when testing SNAPS

    It conforms with OpenStack rules [1] and enforces the same testing
    env over the OPNFV projects [2].

    [1] https://wiki.openstack.org/wiki/Requirements
    [2] https://wiki.opnfv.org/display/functest/Requirements+management

    Change-Id: Iad277b305dbb6c9e96894f5809edcb27a750e418
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/snaps b/docs/submodules/snaps
index c0f1fc7..a6b2166 160000 (submodule)
--- a/docs/submodules/snaps
+++ b/docs/submodules/snaps
@@ -1 +1 @@
-Subproject commit c0f1fc7d39c550f6825b4e323358d44e876c1fa5
+Subproject commit a6b21669ac3a27923cb4053dec645ee9596e1f07