Cannot scroll on Chrome for iPhone if content only contains an image
If the content div contains only an image that extends over the height of the screen (and therefore should be scrollable), attempting to scroll causes the contents of the content div to disappear.

> [test case 1:](http://nickjiang.me/ratchexample/example.html) (single image in content div)
> 
> Before scrolling:
> https://cloud.githubusercontent.com/assets/6390365/4940928/22abc62c-65df-11e4-94d6-e5b4a15c4ae8.png
> 
> After scrolling:
> https://cloud.githubusercontent.com/assets/6390365/4940931/2c30ba90-65df-11e4-99a6-f0f9fbd557e8.png

However, after a certain amount of text is added to the content div (I think enough text so that the content div would be scrollable without the image), the issue disappears, and scrolling works fine:

> [test case 2:](http://nickjiang.me/ratchexample/example2.html) (single image in content div, garbage text below)
> 
> Scrolling:
> https://cloud.githubusercontent.com/assets/6390365/4940973/8e35df4a-65df-11e4-8bd4-88d9d3872936.png

Commenting out the following code in ratchet.css appears to fix the issue:

```
.content > * {
  -webkit-transform: translateZ(0);
      -ms-transform: translateZ(0);
          transform: translateZ(0);
}
```

> [test case 3:](http://nickjiang.me/ratchexample/example3.html) (single image, code snippet commented out)

From what I can tell, the issue only seems to occur on Chrome for iPhone (works fine on Safari).
