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/MockMySensors/MockMySensors.ino

@@ -86,7 +86,7 @@
 
 // Global Vars
 unsigned long SLEEP_TIME = 900000; // Sleep time between reads (in milliseconds)
-boolean metric = true;
+bool metric = true;
 long randNumber;