Use default Honeycomb environment variable names

Per the [`honeycomb-beeline` docs](https://docs.honeycomb.io/getting-data-in/javascript/beeline-nodejs/#optional-configuration), the SDK will automatically pickup `HONEYCOMB_WRITE_KEY` and `HONEYCOMB_DATASET` (no `IO`).  It will also pick up `HONEYCOMB_API_HOST`, used for proxies (like Refinery).

Would it be possible to use these names as the preferred/default source for these values?


