fix spelling mistake in ex_7segment_clock.py

Author: wmalik

Adafruit_LEDBackpack/ex_7segment_clock.py

@@ -23,7 +23,7 @@
   # Set minutes
   segment.writeDigit(3, int(minute / 10))   # Tens
   segment.writeDigit(4, minute % 10)        # Ones
-  # Toggle color
+  # Toggle colon
   segment.setColon(second % 2)              # Toggle colon at 1Hz
   # Wait one second
   time.sleep(1)