Path shortening is implemented incorrectly

[Scripter17]

• Note that this crate implements the URL Standard not RFC 1738 or RFC 3986

When parsing https://example.com/a/c:/.., FireFox gives https://example.com/a/ while the URL crate gives https://example.com/a/c:/.

The shorten_path method seems to be correct except that it calls pop_path, which does nothing if the path segment to be popped is a windows drive letter.

The spec states that shortening a path should only leave a windows drive letter segment alone if it's the only segment in a file:// path, although FireFox seems to instead get that wrong by removing it anyway.