Fixed package name in composer.json (packagist/composer require a lowercase name)

With the former package name being DataTables/DataTables it is not possible to add this library to [packagist](http://packagist.org) which makes this file useless in it's current state.

Please note the [error message](http://img42.imageshack.us/img42/1079/ywi9.png)  when trying to [submit the package](https://packagist.org/packages/submit) to packagist.

"The package name DataTables/DataTables is invalid, it should not contain uppercase characters. We suggest using data-tables/data-tables instead."