used incorrect sensor mode for getbrightness() method

src/sensor.py

@@ -8,7 +8,7 @@ import ev3dev.ev3 as ev3
 class Sensor:
     def __init__(self):
         self._sensor = ev3.ColorSensor()
-        self._sensor.mode = 'REF-RAW'
+        self._sensor.mode = 'COL-REFLECT'
 
     def iscolor(self, color):
         curcol = self._sensor.bin_data("hhh")
@@ -19,7 +19,7 @@ class Sensor:
 
     # see https://stackoverflow.com/questions/687261/converting-rgb-to-grayscale-intensity
     def getbrightness(self):
-        if(self._sensor.mode == 'REF-RAW'):
+        if(self._sensor.mode == 'COL-REFLECT'):
             return self._sensor.value
         else:
             print("ERROR: incorrect sensor mode.")