maxcube: Set MAX! Window Sensor's class to 'window' (#11799)

The sensors are meant to be put on windows to shut down the heating when
windows are open. Having 'window' device class instead of 'opening' is
much more logical here.

homeassistant/components/binary_sensor/maxcube.py

@@ -36,7 +36,7 @@ class MaxCubeShutter(BinarySensorDevice):
     def __init__(self, hass, name, rf_address):
         """Initialize MAX! Cube BinarySensorDevice."""
         self._name = name
-        self._sensor_type = 'opening'
+        self._sensor_type = 'window'
         self._rf_address = rf_address
         self._cubehandle = hass.data[MAXCUBE_HANDLE]
         self._state = STATE_UNKNOWN