Use bool instead of boolean in drivers (#888)

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.

Command:
find drivers -type f | xargs sed -i 's/boolean/bool/g'

drivers/Linux/Stream.cpp

@@ -152,7 +152,7 @@ long Stream::parseInt()
 // this allows format characters (typically commas) in values to be ignored
 long Stream::parseInt(char skipChar)
 {
-	boolean isNegative = false;
+	bool isNegative = false;
 	long value = 0;
 	int c;
 
@@ -190,8 +190,8 @@ float Stream::parseFloat()
 // this allows format characters (typically commas) in values to be ignored
 float Stream::parseFloat(char skipChar)
 {
-	boolean isNegative = false;
-	boolean isFraction = false;
+	bool isNegative = false;
+	bool isFraction = false;
 	long value = 0;
 	int c;
 	float fraction = 1.0;