增加 clean 任务
diff --git a/Makefile b/Makefile
index 24ba11e..4ad93d7 100644
--- a/Makefile
+++ b/Makefile
@@ -5,6 +5,9 @@
 build:
 	$(GRADLE) build -x test
 
+clean:
+	$(GRADLE) clean
+
 test:
 	$(GRADLE) test