add_feed_to_group() is not working - used adafruit_io_groups.py example as a test case.

Running the `adafruit_io_groups.py` example causes the following error:

`Adafruit IO Error 404: not found - API documentation can be found at https://io.adafruit.com/api/docs`

The line causes that error:
https://github.com/adafruit/Adafruit_CircuitPython_AdafruitIO/blob/c9ad360969a4c5f26aa172c2f945b7b389fa4a3c/examples/adafruit_io_http/adafruit_io_groups.py#L68

