use junit test to replace main() for testing

xxl-job-admin/src/test/java/com/xxl/job/admin/core/util/JacksonUtilTest.java

@@ -39,4 +39,4 @@ public class JacksonUtilTest {
         assertThat(result.get("bbb"), Is.<Object>is("222"));
 
     }
-}
+}