fix typo

group_vars/matrix_servers

@@ -9,7 +9,7 @@
 # You can also override ANY variable (seen here or in any given role),
 # by re-defining it in your own configuration file (`inventory/host_vars/matrix.<your-domain>`).
 
-matrix_global_registry: "docker.io/"
+matrix_container_global_registry_prefix: "docker.io/"
 
 ######################################################################
 #