Specify roots in Jest config

[mucsi96]

This PR fixes#7458 by adding roots to Jest configuration. I wanted to add test but didn't found any for Jest configuration. Please let me know what else should I add.

[facebook-github-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need the corporate CLA signed.

If you have received this in error or have any questions, please contact us at cla@fb.com. Thanks!

[mucsi96]

I have now signed the CLA

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[ianschmitz]

Thanks @mucsi96!