fix: aspect ratio of rotated images

[operatorofhell]

Closes: https://github.com/droppyjs/droppy/issues/46

What are the changes and their implications?

When an image is orientated 90 degrees to the left or the right, the width and the height is rotated as well.

Checklist

• [ ] Changes covered by tests (tests added if needed)
• [x] PR submitted to droppyjs.com for any user facing changes