Fix clippy.

src/intermediate/regular_link.rs

@@ -64,8 +64,8 @@ impl LinkTarget {
                     let post_id = parsed.host_str().map(str::to_owned);
                     let subpath = {
                         let subpath = parsed.path();
-                        if subpath.starts_with('/') {
-                            &subpath[1..]
+                        if let Some(subpath) = subpath.strip_prefix('/') {
+                            subpath
                         } else {
                             subpath
                         }