Updated tk-houdini to v1.9.4

Release notes: https://github.com/shotgunsoftware/tk-houdini/wiki/Release-Notes#v194

Author: toolkitty

env/includes/common/engines.yml

@@ -18,7 +18,7 @@ common.engines.tk-3dsmax.location:
 common.engines.tk-houdini.location:
   type: app_store
   name: tk-houdini
-  version: v1.9.3
+  version: v1.9.4
 common.engines.tk-maya.location:
   type: app_store
   name: tk-maya