Update mysql_ro.sql

Author: David Arnold

vault_policy_templates/mysql_ro.sql

@@ -1,3 +1,3 @@
 CREATE USER '{{name}}'@'%' IDENTIFIED BY '{{password}}'; 
-grant SELECT on ${var.db_name}.* to '{{name}}'@'%'; 
+grant SELECT on ${db_name}.* to '{{name}}'@'%'; 
 flush privileges