Definition lincense of MIT in composer

Gregwar/FormBundle defined under the MIT license.

However cannot be shown using composer (& [Packagist](https://packagist.org/packages/gregwar/form-bundle)).

Hope to define the same license in `composer.json`

> $ composer.phar show gregwar/form-bundle

> name     : gregwar/form-bundle
> descrip. : Provides the "entity_id" type (read "entity identifier")
> keywords :
> versions : dev-master
> type     : library
> license  :
> source   : [git] https://github.com/Gregwar/FormBundle.git b71581831996d9c3dc43279a46bd1cd49dca703a
> dist     : [zip] https://api.github.com/repos/Gregwar/FormBundle/zipball/b71581831996d9c3dc43279a46bd1cd49dca703a b71581831996d9c3dc43279a46bd1cd49dca703a
> names    : gregwar/form-bundle