ZOOKEEPER-3649: Add a line break in ls -s CLI

As per the ticket [ZOOKEEEPER-3649](https://issues.apache.org/jira/browse/ZOOKEEPER-3649) we need to add line break ls -s command.

To achieve the desired behavior I have added new line character in option.add of  LsCommand.printChildren(). Please do let me know if made changes gives us the desired behavior or if anything else needs to be changed.

Author: ravowlga123 <ravowlga@gmail.com>

Reviewers: eolivelli@apache.org, andor@apache.org

Closes apache#1183 from ravowlga123/ZOOKEEPER-3649 and squashes the following commits:

f2e1997 [ravowlga123] ZOOKEEPER-3649 Removed additional new line from printChildren
b36d636 [ravowlga123] ZOOKEEPER-3649 Add a line break in ls -s CLI

zookeeper-server/src/main/java/org/apache/zookeeper/cli/LsCommand.java

@@ -127,11 +127,10 @@ private void printChildren(List<String> children, Stat stat) {
             }
             out.append(child);
         }
-        out.append("]");
+        out.append("]\n");
         if (stat != null) {
             new StatPrinter(out).print(stat);
         }
-        out.append("\n");
     }
 
 }