Updated tk-3dsmax to v1.2.6

Release notes: https://github.com/shotgunsoftware/tk-3dsmax/wiki/Release-Notes#v126

Author: toolkitty

env/includes/common/engines.yml

@@ -19,7 +19,7 @@ common.engines.tk-3dsmaxplus.location:
 common.engines.tk-3dsmax.location:
   type: app_store
   name: tk-3dsmax
-  version: v1.2.5
+  version: v1.2.6
 common.engines.tk-houdini.location:
   type: app_store
   name: tk-houdini