Running with karma

Is it possible to use `c8` with `karma`? The repo I'm trying against is https://github.com/chartjs/Chart.js. It shows me coverage of the test setup files, but not the actual source code and I'm not quite sure how to address.

```
$ c8 npx karma start
-------------------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
-------------------|----------|----------|----------|----------|-------------------|
All files | 92.16 | 53.85 | 100 | 92.16 | |
karma.conf.js | 95.74 | 50 | 100 | 95.74 | 18,19,92,93 |
rollup.plugins.js | 89.09 | 55 | 100 | 89.09 |... 45,89,90,95,96 |
-------------------|----------|----------|----------|----------|-------------------|
```

Reproduce the report with `c8 npx karma start` against the referenced Chart.js repository, then inspect `karma.conf.js` and `rollup.plugins.js`, which appear in the coverage output. Compare the collected files with the actual source files and determine whether source coverage is reported; done means the expected source files appear in the coverage report.

Written by the indexing model from the issue text.