Add lifetime comment

src/main.rs

@@ -56,6 +56,7 @@ impl State {
         let rewrite_author = commit.author().email().unwrap() == &self.args.rewrite_email;
 
         let parent_ids: Vec<_> = commit.parent_ids().collect();
+        // This is to deal with lifetime weirdness.
         drop(commit);
 
         let mut new_parent_ids = Vec::new();