cpu/esp_common: Use python3 instead python
cpu/esp_common: Use python3 instead python

yogo1212/RIOT,kaspar030/RIOT,ant9000/RIOT,ant9000/RIOT,authmillenon/RIOT,miri64/RIOT,kaspar030/RIOT,yogo1212/RIOT,jasonatran/RIOT,ant9000/RIOT,OTAkeys/RIOT,yogo1212/RIOT,ant9000/RIOT,jasonatran/RIOT,yogo1212/RIOT,kYc0o/RIOT,basilfx/RIOT,kYc0o/RIOT,kYc0o/RIOT,authmillenon/RIOT,basilfx/RIOT,miri64/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,authmillenon/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,basilfx/RIOT,jasonatran/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,basilfx/RIOT,miri64/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,basilfx/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kaspar030/RIOT,OlegHahm/RIOT,yogo1212/RIOT,authmillenon/RIOT,jasonatran/RIOT,miri64/RIOT,OTAkeys/RIOT