Set the app key in the config after updating it

Set the app key in the config after updating it. This means we can access the app key after setting it with the command.

Currently this code:

```
$this->line(Config::get('app.key'));
$this->call('key:generate');
$this->line(Config::get('app.key'));
```

will produce:

```
YourSecretKey!!!
Application key [bnoEpWg645Ttdew6YJVuQv658NMbgkQ4] set successfully.
YourSecretKey!!!
```

but a better behaviour would be to do this:

```
YourSecretKey!!!
Application key [bnoEpWg645Ttdew6YJVuQv658NMbgkQ4] set successfully.
bnoEpWg645Ttdew6YJVuQv658NMbgkQ4
```