Update LsTool.java

If we define args as null in the constructor, we won't be able to call args.length (since it will throw a Null Pointer Exception). So instead of checking args.length == 0, I change it to check args.length == 1 where args[0] will be "ls"... I have told David to use this new constructor also in the parsing part...
Merge pull request #2 from andriantolie/patch-2

Update LsTool.java