Fix magento-hackathon minimum stability

Hi, I encountered a problem while using composer to integrate AvS_FastSimpleImport into a Magento project. There was a minimum stability conflict between the requirements of FastSimpleImport (specifying a dev-master requirement for magento-hackathon/magento-composer-installer) and other dependencies that required a stable version of it.
I edited the composer.json file to change the requirement for magento-composer-installer from "dev-master" to "*", meaning that now any version satisfying the minimum stability setting will be accepted.

See for example "https://github.com/EcomDev/EcomDev_PHPUnit" and "https://github.com/magento-hackathon/Magento-PSR-0-Autoloader".