title: Idle timer python dbus insue when using crontab or ssh
body: <p>i have this folowing script:</p>
  
  <pre><code>from idle_time import IdleMonitor
  idle = None
  try:
      monitor = IdleMonitor.get_monitor()
      idle = monitor.get_idle_time()
  except:
      idle = None
  
  print(idle)
  </code></pre>
  
  <p>this is returning me a erro when i try to execute trought a ssh or in crontab</p>
  
  <pre><code>Could not load &lt;class 'idle_time.GnomeWaylandIdleMonitor'&gt;
  Traceback (most recent call last):
    File "/usr/local/lib/python3.7/dist-packages/idle_time/__init__.py", line 31, in get_monitor
      return monitor_class(**kwargs)
    File "/usr/local/lib/python3.7/dist-packages/idle_time/__init__.py", line 83, in __init__
      self.connection = connect_and_authenticate(bus="SESSION")
    File "/usr/local/lib/python3.7/dist-packages/jeepney/integrate/blocking.py", line 113, in connect_and_authenticate
      bus_addr = get_bus(bus)
    File "/usr/local/lib/python3.7/dist-packages/jeepney/bus.py", line 53, in get_bus
      return find_session_bus()
    File "/usr/local/lib/python3.7/dist-packages/jeepney/bus.py", line 42, in find_session_bus
      addr = os.environ['DBUS_SESSION_BUS_ADDRESS']
    File "/usr/lib/python3.7/os.py", line 678, in __getitem__
      raise KeyError(key) from None
  KeyError: 'DBUS_SESSION_BUS_ADDRESS'
  </code></pre>
  
  <p>how to fix it? or get idletime from linux with crontab</p>