Fixing composer to not require CakePHP

Since this project is a CakePHP Plugin its best to not require cakephp in the composer file since it's implied that CakePHP is installed if you are installing a CakePHP Plugin. Having this require duplicates the cakephp libs folder and wastes space. You can look at other major plugins and see their composer file does not require cakephp https://github.com/CakeDC/migrations/blob/master/composer.json https://github.com/cakephp/debug_kit/blob/master/composer.json