Smoother scrolling on older iOS devices (#1654)

This may address the scrolling issues mentioned here: https://github.com/tootsuite/mastodon/issues/1622

app/assets/stylesheets/components.scss

 @import 'variables';
 
 .app-body{
+ -webkit-overflow-scrolling: touch;
  -ms-overflow-style: -ms-autohiding-scrollbar;
 }