Updated tk-multi-publish2 to v2.6.4

Release notes: https://github.com/shotgunsoftware/tk-multi-publish2/wiki/Release-Notes#v264

Author: Toolkitty

env/includes/common/apps.yml

@@ -35,7 +35,7 @@ common.apps.tk-multi-setframerange:
 common.apps.tk-multi-publish2.location:
   type: app_store
   name: tk-multi-publish2
-  version: v2.6.3
+  version: v2.6.4
 common.apps.tk-multi-loader2.location:
   type: app_store
   name: tk-multi-loader2