Update app.py

Didn't save the sentiment.csv for the data vizualizer to use.

app.py

@@ -327,6 +327,9 @@ def sentiment_analyzer(csv_file_name='combined_news_response.csv'):
       'sentiment': [sentiment_mapping[sent] for sent in sentiments]
   })
 
+  sentiment_df.to_csv('sentiment.csv')
+  print(f'Sentiment df saved as "sentiment.csv"')
+
   return sentiment_df