Really this just removes references to polyfill.io from documentation

Adds a non-transpiled version of the library to the module field in `package.json.

See v2.2.1 notes.

In v2.2.0 we accidentally added a non-transpiled version of the polyfill to the module field in package.json. Bundlers like webpack will prefer this version over the main version so this broke users of webpack who were relying on that behavior (issue).

v2.2.1 fixes this by pointing the module field at a transpiled version. We still plan to release a non-transpiled, ESM version, but we'll do so as a breaking change in v3.