Change Jest configuration to also work on Windows

[StephanBijzitter]

Summary

Due to Windows file paths, jest wasn't able to find any test files and due to rm not being available on Windows, coverage could not be created.

Updating the test matcher and replacing rm with rimraf (a node dependency) allows Windows to run this project properly when developing locally

Requirements (place an x in each [ ])

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [ ] I've written tests to cover the new code and functionality included in this PR.
• [x] I've read, agree to, and signed the Contributor License Agreement (CLA).

[CLAassistant]

All committers have signed the CLA.

[melloware]

Thank you for this. I implemented your changes in my fork: https://github.com/melloware/csp-webpack-plugin