Does not work with __coverage__ or istanbul

I get this error
```
Error: file.js: Could not statically evaluate how the fs module was required/imported. while parsing file: file.js
```
When trying to use `static-fs` with either [babel-plugin-static-fs](https://www.npmjs.com/package/babel-plugin-static-fs) or [babel-plugin-istanbul](https://github.com/istanbuljs/babel-plugin-istanbul)

Reproduce the error from file.js using static-fs with babel-plugin-static-fs and babel-plugin-istanbul. Start by comparing how each plugin processes the fs import or require, then verify that the combined setup no longer reports the static-evaluation error.

Written by the indexing model from the issue text.