Remove unnecessary closure

src/routes.rs

 ) -> Result<status::Created<Json<Snippet>>, Status> {
     snippet::insert(snippet.into_inner(), &connection)
         .map(|snippet| status::Created(String::from(""), Some(Json(snippet))))
-        .map_err(|error| error_response(error))
+        .map_err(error_response(error)
 }