Examples: Update ADC()

[helgibbons]

Should help with #965

[helgibbons]

I've not done anything with our Analog class in modules_py/pimoroni.py here, which might also need looking at?

[Gadgetoid]

Thank you!

I guess in Analog it should be something like:

self.pin = ADC(pin) if isinstance(pin, Pin) else ADC(Pin(pin))

Looks like it's never actually called with a Pin instance, but it should probably handle that just in case.