fix: sort items before chunking

The chunk_by function works like coreutils sort in that it expects
sorted inputs.

src/main.rs

@@ -27,7 +27,8 @@ async fn complete(mut channel: Channel, client: &Client) -> Result<Box<Channel>>
     let grouped: Vec<Vec<rss::Item>> = channel
         .items()
         .iter()
-        .chunk_by(|item| get_domain(item))
+        .sorted_by(|a, b| get_domain(a).cmp(&get_domain(b)))
+        .chunk_by(|&item| get_domain(item))
         .into_iter()
         .map(|(_k, v)| v.cloned().collect())
         .collect();