Missing mysql driver in docker_laravel cookbook docker image?

@crigor

Heads up, looks like your docker image is missing the MySQL PDO driver..

- [master](https://github.com/engineyard/ey-docker-recipes/blob/master/cookbooks/docker_laravel/recipes/default.rb#L6) (or: [permalink in case master changes](https://github.com/engineyard/ey-docker-recipes/blob/fc32b112e8698f12c9fed970d1efab0cd57d61d3/cookbooks/docker_laravel/recipes/default.rb#L6))
- https://hub.docker.com/r/crigor/quickstart_laravel/

After booting an instance, if I try to `GET /` a laravel error `Whoops, looks like something went wrong.` appears, and dumps the following to logs.

```
PDOException: could not find driver in /usr/src/app/vendor/laravel/framework/src/Illuminate/Database/Connectors/Connector.php:55
```

I ran the following code to test for drivers:

```php
';
}

## output:
## pgsql
```

MySQL was not on the list.

Thanks a lot for excellent work on EY docker support, this some seriously cool and useful stuff! :)