Update examples for legal I2C addresses

examples/master_reader/master_reader.ino

 
 void loop()
 {
-  Wire.requestFrom(2, 6);    // request 6 bytes from slave device #2
+  Wire.requestFrom(8, 6);    // request 6 bytes from slave device #8
 
   while(Wire.available())    // slave may send less than requested
   { 

examples/master_writer/master_writer.ino

 
 void loop()
 {
-  Wire.beginTransmission(4); // transmit to device #4
+  Wire.beginTransmission(8); // transmit to device #8
   Wire.write("x is ");        // sends five bytes
   Wire.write(x);              // sends one byte  
   Wire.endTransmission();    // stop transmitting

examples/slave_receiver/slave_receiver.ino

 
 void setup()
 {
-  Wire.begin(4);                // join i2c bus with address #4
+  Wire.begin(8);                // join i2c bus with address #8
   Wire.onReceive(receiveEvent); // register event
   Serial.begin(9600);           // start serial for output
 }

examples/slave_sender/slave_sender.ino

 
 void setup()
 {
-  Wire.begin(2);                // join i2c bus with address #2
+  Wire.begin(8);                // join i2c bus with address #8
   Wire.onRequest(requestEvent); // register event
 }