Fix gr import

app.py

@@ -3,6 +3,8 @@ from vietTTS.hifigan.mel2wave import mel2wave
 from vietTTS.nat.text2mel import text2mel
 from vietTTS import nat_normalize_text
 import numpy as np
+import gradio as gr
+
 
 import os
 os.system("gdown --id 16UhN8QBxG1YYwUh8smdEeVnKo9qZhvZj -O duration_latest_ckpt.pickle")