tests fail to run

Thanks for making this project. When I run `yarn test` or `npm run test`, I get an error:

Validation Error:

Module /Users/joshua/Projects/create-react-app-parcel/node_modules/create-react-app-parcel-typescript/config/polyfills.js in the setupFiles option was not found.

Configuration Documentation:
https://facebook.github.io/jest/docs/configuration.html

If I install the npm module raf-polyfill, and then manually copy the contents of node_modules/raf-polyfill/raf.js to node_modules/create-react-app-parcel-typescript/config/polyfills.js, I can run the tests properly.

Reproduce the failure with `yarn test` or `npm run test`, then inspect the Jest `setupFiles` reference to `config/polyfills.js` and the reported `raf-polyfill` workaround. Done means the project tests run successfully without manually copying files into `node_modules`.

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