Updated test output from image-transform (#513)

ref #485

- The update to Sharp from 0.32 to 0.34 has resulted in some minor differences
- The images are slightly smaller, but look the same to my eye
- Added a note about how to view the changes

Author: ErisDS

packages/image-transform/README.md

@@ -31,6 +31,7 @@ Follow the instructions for the top-level repo.
 - `yarn lint` run just eslint
 - `yarn test` run lint and tests
 
+If the image output changes, one way to compare the output is with [git diff image](https://github.com/ewanmellor/git-diff-image)