Support for webworkers

http-browserify [assumes a normal browser window](https://github.com/substack/http-browserify/blob/11bfdeac2534fafbd5819bda96fa32f01802b6cc/index.js#L46) and not a worker, though http requests in a worker are legitimate

inside a webworker the global object is `self` not `window`

Start with index.js at the linked line, where http-browserify assumes a normal browser window. Check the worker context described in the issue, where the global object is self, and verify that HTTP requests work there as well as in a normal browser window.

Written by the indexing model from the issue text.