add punkt tokenizer

app.py

@@ -120,6 +120,7 @@ def find_source(text, docs):
 @st.experimental_singleton
 def init_models():
     nltk.download('stopwords')
+    nltk.download('punkt')
     from nltk.corpus import stopwords
     stop = set(stopwords.words('english') + list(string.punctuation))
     device = torch.device("cuda" if torch.cuda.is_available() else "cpu")