Update app.py

app.py

@@ -89,7 +89,7 @@ def create_bibtex_entry(data):
     match_year = re.search(r'\b(\d{4})\b', data['year'])
     
     if match_year:
-        data['year'] = match.group(1)
+        data['year'] = match_year.group(1)
         year = data['year']
     else:
         data.pop('year', '')