Update constants.dart

Author: Yugesh-Kumar-S

lib/constants.dart

@@ -169,4 +169,4 @@ String builtIn = 'Built-In';
 String lx = 'Lx';
 String maxScaleError = 'Max Scale';
 String lightSensorError = 'Light sensor error:';
-String lightSensorInitialError = 'Failed to initialize light sensor:';
+String lightSensorInitialError = 'Failed to initialize light sensor:';