update doc

Author: Nicole00

client/src/main/java/com/vesoft/nebula/driver/graph/net/NebulaClient.java

@@ -172,7 +172,7 @@ public synchronized void close() {
     /**
      * get the Client status
      *
-     * @reuturn true if client is closed
+     * @return true if client is closed
      */
     public boolean isClosed() {
         return isClosed;