small typo fix

Author: ladyada

Adafruit_I2CDevice.cpp

@@ -69,7 +69,7 @@ bool Adafruit_I2CDevice::detected(void) {
   _wire->beginTransmission(_addr);
 #ifdef DEBUG_SERIAL
   DEBUG_SERIAL.print(F("Address 0x"));
-  DEBUG_SERIAL.print(_addr);
+  DEBUG_SERIAL.print(_addr, HEX);
 #endif
   if (_wire->endTransmission() == 0) {
 #ifdef DEBUG_SERIAL