Added bootstrap requirement and branch-alias

[bootswatch] / composer.json

{
    "name": "thomaspark/bootswatch",
    "description": "Themes for Twitter Bootstrap",
    "license": "Apache",
    "authors": [
        {
            "name": "thomaspark",
            "email": "hello@thomaspark.me"
        }
    ],
    "require": {
        "slywalker/twitter_bootstrap": "dev-master"
    },
    "extra": {
        "branch-alias": {
            "dev-master": "gh-pages"
        }
    }
}