Conversion from http::Request to http_types::Request fails

When converting an `http::Request` from `hyper` to an `http_types::Request` the `url` fails to convert with an error:

```rust
relative URL without a base
```

small example problem showing the failure:

```rust
use std::convert::TryFrom;

fn main() {
let request = http::Request::builder()
.method("GET")
.uri("/")
.header("Host", "localhost")
.body(http_types::Body::empty())
.unwrap();

http_types::Request::try_from(request).unwrap();
}
```