update Makefile

Makefile

@@ -10,7 +10,7 @@ status:
 	@ps -ef | grep infer.py | grep -v grep
 
 kill:
-	@ps -ef | grep infer.py | grep -v grep | awk '{print $2}' | xargs kill
+	@$(ps -ef | grep infer.py | grep -v grep | awk '{print $2}' | xargs kill)
 
 log:
 	@tail -f log/runtime.log