query params keep on getting added to the end

I'm calling `navigate!` with the same `route` and `params`, but changing the 3rd argument, the `query`, causes a new set of query params to be added to the end of the URL. (instead of clearing out the previous keys).

For example, from the README if I do
```
(r/navigate! router :myapp/user-by-id {:id 2} {:foobar 1})
;; => "/api/users/2?foobar=1"

(r/navigate! router :myapp/user-by-id {:id 2} {:foobar 2})
;; => "/api/users/2?foobar=1?foobar=2"

```