Update MIDI specification link in the documentation

src/common.rs

@@ -278,7 +278,7 @@ impl MidiOutputConnection {
  }
 
  /// Send a message to the port that this output connection is connected to.
- /// The message must be a valid MIDI message (see https://www.midi.org/specifications/item/table-1-summary-of-midi-message).
+ /// The message must be a valid MIDI message (see https://www.midi.org/specifications-old/item/table-1-summary-of-midi-message).
  pub fn send(&mut self, message: &[u8]) -> Result<(), SendError> {
  self.imp.send(message)
  }