RequestBuilder::build creates a url with extra '& at the end

[hmacias-avaya]

Describe the Bug

When creating a request that contains query parameters, for example

let url = "http://something.com/get?param1=value1";
let request = Request::get(url).build().unwrap();

the request created will target http://something.com/get?param1=value1& and not the original url, http://something.com/get?param1=value1 (note there is an '&' added).

Steps to Reproduce

See code above. Also I've provided a test on the PR #497

Expected Behavior

The created request should have exactly the same url that was given as a parameter.

Actual Behavior

A '&' has been added to the end of the url.