add flac MIME type

src/vfs/physical.rs

@@ -103,6 +103,7 @@ fn guess_content_type(extension: &str) -> Option<&'static str> {
         "png" => Some("image/png"),
         "webp" => Some("image/webp"),
         "jpg" | "jpeg" => Some("image/jpeg"),
+        "flac" => Some("audio/flac"),
         _ => None,
     }
 }