Documented option not actually implemented

[neilvanlandingham]

Thanks for the great plugin, Surma!

The README.md specifies that there is an option workerRegexp exposed for customizing the regular expression assigned to workerRegexpForTransform in index.js, but this hasn't actually been implemented in the code.

I came across this issue because rollup is for some reason transforming import.meta.url in my code to importMeta.url causing the default workerRegexpForTransform not to match in my use case.