Update app.py

Join only really small sentences.

app.py

@@ -26,7 +26,7 @@ def split_to_parts(text):
     index = 0
     for s in text:
         parts[index] += s
-        if s in split_symbols and len(parts[index]) > 150:
+        if s in split_symbols and len(parts[index]) > 20:
             index += 1
             parts.append('')
     return parts