AVRISP mkII should use option avrispmkii.communication=serial

In programmers.txt, AVRISP mkII has the option avrispmkii.communication=usb. However, at least on my Linux systems, this does not work as avrdude fails to find any devices, outputting the following error message:

```
avrdude: usbdev_open(): did not find any USB device "usb"
```

Apparently, the serial port chosen in Arduino IDE is not used in the avrdude command. Instead, the parameter "-Pusb" is used. When the setting in question is changed to avrispmkii.communication=serial, avrdude is passed the chosen serial port and burning a bootloader works.