Fix clippy warnings, update dependencies (#91)

src/compressor/stats_tests.rs

@@ -145,11 +145,7 @@ fn stats_correct_if_no_changes() {
         let pred_group = initial_edges.get(&i);
 
         // Need Option<i64> not Option<&i64>
-        let prev;
-        match pred_group {
-            Some(i) => prev = Some(*i),
-            None => prev = None,
-        }
+        let prev = pred_group.copied();
 
         // insert that edge into the initial map
         initial.insert(