Update app.py

app.py

@@ -46,7 +46,7 @@ def write_song():
                start_times=[0, 0, 4, 8],
                bpm=165)
     #current_daw.play(result)
-    current_daw.export(current_song, filename='song.wav') # export the piece type current_song to
+    current_daw.export(result, filename='song.wav') # export the piece type current_song to
     # a wav file named "my first song.wav"
     return 'song.wav'