NYC Reporting and Source Map Bug

Repro steps

1. clone this repo
2. npm i
3. npm run build
4. cd build
5. npx nyc ./static ./static-i
6. rename static to static-o, static-i to static
7. npx serve
8. open chrome to localhost:5000
9. in dev tools console, JSON.stringify(__coverage__)
10. copy data into .nyc_output/out.json
11. npx nyc report --reporter=html
12. open coverage/index.html
13. report here looks good
14. click into any of the .js files
15. cry a little