Download 8 fragments in parallel.

src/main/java/moe/nekojimi/chords/Downloader.java

@@ -357,6 +357,7 @@ public class Downloader extends QueueThing<TrackRequest, Track>
                     + " --audio-format=wav"
                     + " --no-playlist"
                     //                    + " --extractor-args youtube:player_client=android"
+                    + " -N 8"
                     + " -o " + getDownloadDir().getAbsolutePath() + "/%(title)s.%(ext)s "
                     + request.getUrl().toString();