feat: add typescript support - #14

Wow, thanks for the quick PR. Looks solid! Unfortunately it seems like this upgrade broke something. Here's how to reproduce.

I made this repo back then to be able to play with jsdom-screenshot. I tried it with this version and it seems like some styles can't be loaded.

Steps:

git clone git@github.com:dferber90/visual-regression-testing-example.git
cd visual-regression-testing-example
yarn
yarn test --watch

Tests will probably fail now due to differences of our laptops, so press u once to update them. This will be the base of comparison now. You can commit the updated tests locally, so you see the real diff after switching the library your version later on.

In the TypeScript version of jsdom-screenshot, run

yarn build
yarn link

Now back in the visual-regression-testing-example folder, run

yarn link jsdom-screenshot
yarn test --no-cache 

The tests will fail now, but they should pass as nothing should change by switching to the TypeScript version. Open src/__image_snapshots__/__diff_output__/. You should now see the diff this upgrade causes. It seems like some styles can't be loaded.

Can you look into that?