Enable ZookeeperMetadataReportTest (#3360)

Author: biyuhao

dubbo-metadata-report/dubbo-metadata-report-zookeeper/src/test/java/org/apache/dubbo/metadata/store/zookeeper/ZookeeperMetadataReportTest.java

@@ -38,7 +38,6 @@
 /**
  * 2018/10/9
  */
-@Disabled("Keeps fail on Travis")
 public class ZookeeperMetadataReportTest {
     private TestingServer zkServer;
     private ZookeeperMetadataReport zookeeperMetadataReport;