Fix blurry CVImageElement drawing on high dpi (>1.0) displays

[richardhenry]

The canvas renderer CVImageElement draws blurry images on high dpi displays, like this example where the dpi is 2.0:

This diff changes the implementation so that images draw correctly:

I'm not sure if this is the optimal fix, but it seems to work.

[bodymovin]

hey thanks for the PR! If I understand it correctly, you're drawing the img directly to the canvas and dropping the buffer canvas, is that right?
(btw, can you update the PR without building the files?)