model01: Use a modified CDC.cpp

At least for OSX, we need to slow down Serial writes. The easiest way to do that
is to add a delay after each write, and to accomplish that, the easiest is to
modify `CDC.cpp`. Without this, on OSX, we end up writing  too fast (and
changing the baud rate does not help, no matter in which direction I change),
and end up losing data.

This is not a great solution. It's not even a solution, but a workaround. But it
works for now.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

avr/variants/model01/CDC.cpp

@@ -232,6 +232,7 @@ size_t Serial_::write(const uint8_t *buffer, size_t size)
 	if (_usbLineInfo.lineState > 0)	{
 		int r = USB_Send(CDC_TX,buffer,size);
 		if (r > 0) {
+			delay(5);
 			return r;
 		} else {
 			setWriteError();