URLの最後に ?s=ピルクセル数 をつける 100px(https://www.gravatar.com/avatar/d9669165d1baf624cedab4afc3dfcc42?s=100) 200px(https://www.gravatar.com/avatar/d9669165d1baf624cedab4afc3dfcc42?s=200) 参考 Gravatar/Image Requests
