Documentation forwarding to old CircuitPython version

[makermelissa]

The link to the documentation (https://docs.circuitpython.org/) forwards to CircuitPython 8 documentation. I couldn't find where this is set up, but it should be changed to 9.0.0 now that it is released.

[tannewt]

I've updated it to latest since it'll be similar to 9.0. It is in the RTD project admin settings under "default version".