Fix min_microversion in volume test_groups_rbac

This PS fixes the min_microversion in volume test_groups_rbac
which is incorrectly 3.14 when in fact it should be 3.13 [0] according
to Cinder microversion documentation. This change will also make Patrole
consistent with Tempest [1].

[0] https://docs.openstack.org/cinder/latest/contributor/api_microversion_history.html#id13
[1] https://github.com/openstack/tempest/blob/c536175d8d4d572278b4e592dadc548b34e4ea91/tempest/api/volume/admin/test_groups.py#L27

Change-Id: I9b19d44e25057d688e4b968cab2a047049658344
diff --git a/patrole_tempest_plugin/tests/api/volume/test_groups_rbac.py b/patrole_tempest_plugin/tests/api/volume/test_groups_rbac.py
index 86ea356..7f1010f 100644
--- a/patrole_tempest_plugin/tests/api/volume/test_groups_rbac.py
+++ b/patrole_tempest_plugin/tests/api/volume/test_groups_rbac.py
@@ -64,7 +64,7 @@
 
 
 class GroupsV3RbacTest(BaseGroupRbacTest):
-    min_microversion = '3.14'
+    min_microversion = '3.13'
     max_microversion = 'latest'
 
     @decorators.idempotent_id('43235328-66ae-424f-bc7f-f709c0ca268c')