Fix for error triggering on some /tr commands.

If someone only types 2 arguments, then the args[] array from OnCommand only contains 2 arguments.
If you check for args[2] == null it will throw an arrayIndexOutOfbounds exeption because there are only 2 elements in the array.
Merge pull request #5 from Taeir/patch-3

Fix for error triggering on some /tr commands.