fix(rule_engine.hrl): Type spec, args map is keyed by binary

apps/emqx_rule_engine/include/rule_engine.hrl

@@ -60,7 +60,7 @@
         { id :: action_instance_id()
         , name :: action_name()
         , fallbacks :: list(#action_instance{})
-        , args :: #{atom() => term()} %% the args got from API for initializing action_instance
+        , args :: #{binary() => term()} %% the args got from API for initializing action_instance
         }).
 
 -record(rule,