Solved problem with redirects that returne a request for an unresolved r...

Hello @ForbesLindesay 

I am using this library as a dependency for sync-request for a course at university and found a bug with certain redirects that, when the location header response was a relative path, made http-basic crash as follows:

sync-request/node_modules/then-request/node_modules/http-basic/index.js:143
  var req = protocols[url.protocol.replace(/\:$/, '')].request({

I solved the issue by just doing a url resolve on the location header field using the previous url.

Hope you consider it.

Cheers!