Use warp 0.3

[tokahuke]

This crate currently uses warp 0.2, but I am using 0.3. I am getting version conflicts.

    |
216 | /     impl<FN, F> FilterBase for WithLog<FN, F>
217 | |     where
218 | |         FN: Fn(Info) + Clone + Send,
219 | |         F: Filter + Clone + Send,
...   |
234 | |         }
235 | |     }
    | |_____^
= note: perhaps two different versions of crate `warp` are being used?

I will open a PR.