The purpose of doing this was to avoid i2c conflicts. It has no affect on how the code runs. You can still run it using busio.i2c, but using board.i2c is preferable.
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://circuitpython.org/libraries).
To use in CPython, `pip3 install adafruit-circuitpython-gps`.
Read the [docs](http://circuitpython.readthedocs.io/projects/gps/en/latest/) for info on how to use it.