fix zk permission

.travis.yml

@@ -48,7 +48,7 @@ before_script:
   - curl -sfL https://raw.githubusercontent.com/bilibili/discovery/master/cmd/discovery/discovery-example.toml -o $GOPATH/bin/discovery.toml
   - nohup bash -c "$GOPATH/bin/discovery -conf $GOPATH/bin/discovery.toml &"
   # zookeeper
-  - ./apache-zookeeper-${ZK_VERSION}-bin/bin/zkServer.sh start ./zk/conf/zoo_sample.cfg 1> /dev/null
+  - sudo ./apache-zookeeper-${ZK_VERSION}-bin/bin/zkServer.sh start ./zk/conf/zoo_sample.cfg 1> /dev/null
 
 script:
   - go build ./...