Add missing comma to the changes.json JSON array

Fixes the following error:

```
$ php artisan changes
{"error":{"type":"ErrorException","message":"Argument 1 passed to Illuminate\\Foundation\\Console\\ChangesCommand::getChangeVersion() must be of the type array, null given, called in \/Users\/andrew\/Sites\/app.local.leve.rs\/vendor\/laravel\/framework\/src\/Illuminate\/Foundation\/Console\/ChangesCommand.php on line 30 and defined","file":"\/Users\/andrew\/Sites\/app.local.leve.rs\/vendor\/laravel\/framework\/src\/Illuminate\/Foundation\/Console\/ChangesCommand.php","line":77}}
```

Also thought about writing a quick unit test for it to make sure it can be decoded properly. But there aren't any unit tests for any of the commands to tack onto.