Support big screenshot

[ryuran]

Environment (please complete the following information):

• webdriver-image-comparison version: 0.13.2

Describe the bug Web driver Image fail on big images.

Given error :

invalid value (typically too big) for the size of the input (surface, pattern, etc.)

https://github.com/Automattic/node-canvas/issues/1374

To Reproduce Try with an image ~40000px long.

Expected behavior webdriver-image-comparison should be able to manage big images (useful for full page screen shot).

Log

invalid value (typically too big) for the size of the input (surface, pattern, etc.)

Additional context this comment advice to split the image to avoid this issue.

[wswebcreation]

Thanks for this issue, I'll take a look at it when I have some more time