Doesn't correctly handle anchor urls

[McPo]

First of all, thanks for the great library. It is also especially important as while react-router v4.x.x is stated to be getting relative links, no new features will be backported to v3.x.x, so its great that this library exists.

I noticed an issue when using this in conjunction with react-router-scroll, which allows anchor tags to be placed in the URL.

If I was to visit a url with an anchor tag /helloworld#foo

and then click a relative link of ./bar, the result would be /helloworld#foo/bar

Which isn't a valid URL, instead I would've expected /helloworld/bar