Derive config from .nycrc

[bennypowers]

I'd like to add a .nycrc.json in my project root and have karma-coverage pick up on it without needing to specify includes or excludes in my karma.conf.js

Example config:

{
  "include": ["src/**/*.js"],
  "exclude": [
    "**/*.test.js",
    "stories/*",
    "test/*"
  ]
}

Additionally, some users will want to specify a nyc key in their package.json with value same as above.

[bennypowers]

related to istanbuljs/nyc#320