Fixed hub file writing

src/hub.py

@@ -69,7 +69,7 @@ def timer_stop(msg):
     now = time.time()
     name = msg['from'] + msg['id']
     if name in timers:
-        with open('time_differences', 'w') as f:
+        with open('time_differences', 'a') as f:
             f.write(f'{msg["from"]},{now - timers[name]}')