fix bug on Chrome on Android
fix bug on Chrome on Android

修正在Android版Chrome上發生的臭蟲：
bottom part of the game is out of screen
遊戲畫面的底部會跑出畫面

it is the bug fix
https://bugs.chromium.org/p/chromium/issues/detail?id=428132
that introduces this bug

stdio2016/shapeclear-html,stdio2016/shapeclear-html,stdio2016/shapeclear-html,stdio2016/shapeclear-html