Reduce self-heating

[ben-lewis]

As with the equivalent C++ library https://github.com/adafruit/Adafruit_MAX31865, the bias current seems to be left on permanently, leading to increased self-heating. Adding self.bias = False at line 233 of adafruit_max31865.py should fix this. Also, maybe a note should be made that all improvements to C++ libraries should be duplicated in the equivalent python library and vice versa.

[tannewt]

@ben-lewis Would you mind making a PR with this change? Thanks! Instructions are here: https://learn.adafruit.com/contribute-to-circuitpython-with-git-and-github

[ben-lewis]

#23

[jposada202020]

@ben-lewis Could this be closed now the changes were merged? thanks :)