[ios app] Board too far from thumbs

[morganiq]

Prior to discovering your native app, I played with an app called "2048+" for some time, which had the closest look and feel I could find to the original web app when I went looking for one. That app positions the board within comfortable reach for thumbs, slightly below center; your native app positions the board slightly above center, and requires reaching or shifting the phone downward to play reliably. (Note that having to shift the phone in your hand can compound the swipe triggering issues mentioned in a different thread.) Please shift the board down to a more comfortable location. (iPhone 6 screen size.)