mapFileCoverage = fileCoverage => {
  fileCoverage.path = fileCoverage.path.replace(
    /(.*packages\/.*\/)(build)(\/.*)/,
    '$1src$3',
  );
  return fileCoverage;
}
Because we have a build step, sometimes we can test files from both
`packages/metro-whatever/build/*` and `packages/metro-whatever/src/*`

If we require file by its relative path like:
   // inside `metro-whatever/src/__tests__/index.js`
   require('../index.js'); // this will require `metro-whatever/src/index.js`

But if we require it by a package name, this will go through node_modules
and lerna index.js link. So the actual file will be required from `build/`
   // inside another packages
   // this will go through lerna and require `metro-whatever/build/index.js
   require('metro-whatever')

these files are identical (one is preprocessed, another is transformed on
the fly), but the coverage paths are different.
This script will map coverage results from both locations to one and
produce a full coverage report.