Cobertura XML is malformed: unescaped quotes in filename string

* **Version**: v12.18.3
* **Platform**: Linux d35e72cef690 5.4.72-microsoft-standard-WSL2 #1 SMP Wed Oct 28 23:40:43 UTC 2020 x86_64 GNU/Linux

I'm guessing this is a trivial matter of needing to escapify filenames, but am happy to help produce a minimal repro if it would be helpful.

The malformed XML is an unquoted string that occurs when our coverage run includes a webpack'ed bundle that references react as an external module:
```

```

(PS - Great project!)