composer.json generates errors to composer install/update

Hi!

Requiring:

    "require": {
        "sensio/generator-bundle": "2.1.x-dev"
    },

generates dependency error on Symfony 2.1.6. I'd had to clone locally, changes symfony's composer.json to point to this local repository after change the bundle's composer.json to:

    "require": {
        "sensio/generator-bundle": "2.1.*"
    },

and then it worked. 

My pull request do that thing.

Thanks for the bundle!

Rafael Goulart from Brazil