Require Python version >= 3.7.0

Spawned from #81, but for using the same Python version as the Blinka requirement of >= 6.20.6

Author: tekktrik

setup.py

@@ -34,6 +34,7 @@
  # Author details
  author="Adafruit Industries",
  author_email="circuitpython@adafruit.com",
+ python_requires=">=3.7.0",
  install_requires=["Adafruit-Blinka>=6.20.4", "adafruit-circuitpython-typing"],
  # Choose your license
  license="MIT",