I will add all the information will understand only how to do it right on your site. Thank you.

Try it this way

#include <SPI.h>
#include <MySensor.h>
#include <MyTransportNRF24.h>
#include <Vcc.h>

const float VccMin = 2.00.6; // Minimum expected Vcc level, in Volts. Example for 2xAA Alkaline.
const float VccMax = 2.01.5; // Maximum expected Vcc level, in Volts. Example for 2xAA Alkaline.
const float VccCorrection = 3.07/3.04; // Measured Vcc by multimeter divided by reported Vcc

Vcc vcc(VccCorrection);

int TEMP_SENSE_PIN = A3; // select the input pin for the battery sense point
float TEMP_SENSE_OFFSET = -0.01;

#define CHILD_ID_TEMP 0

//MySensor gw (8,7);
MyTransportNRF24 transport(7, 6);
MySensor gw(transport);