Use bool instead of boolean in examples

In the Arduino IDE, boolean is an alias for bool.
The Arduino IDE might deprecate boolean in the future, see
https://github.com/arduino/Arduino/issues/4673 for details.

examples/WaterMeterPulseSensor/WaterMeterPulseSensor.ino

@@ -65,7 +65,7 @@ double ppl = ((double)PULSE_FACTOR)/1000;        // Pulses per liter
 volatile unsigned long pulseCount = 0;   
 volatile unsigned long lastBlink = 0;
 volatile double flow = 0;  
-boolean pcReceived = false;
+bool pcReceived = false;
 unsigned long oldPulseCount = 0;
 unsigned long newBlink = 0;   
 double oldflow = 0;