build(package): Add unpkg field to package.json (#300)
build(package): Add unpkg field to package.json (#300)

unpkg.com, a NPM CDN, uses an unpkg field, then the browser field (undocumented), and then the main
field to find a package's entry point. By adding the unpkg field, simple-statistics will only rely
on unpkg's documented behavior.
simple-statistics/simple-statistics,simple-statistics/simple-statistics,simple-statistics/simple-statistics,tmcw/simple-statistics