Drop support for EOL Python 3.7

Author: hugovk

README.md

@@ -1,7 +1,7 @@
 # strava-tools
 
 [![GitHub Actions status](https://github.com/hugovk/strava-tools/workflows/Lint/badge.svg)](https://github.com/hugovk/strava-tools/actions)
-[![Python: 3.6+](https://img.shields.io/badge/Python-3.6+-blue.svg?logo=python&logoColor=FFE873)](https://www.python.org/downloads/)
+[![Python: 3.8+](https://img.shields.io/badge/Python-3.8+-blue.svg?logo=python&logoColor=FFE873)](https://www.python.org/downloads/)
 [![Code style: Black](https://img.shields.io/badge/code%20style-Black-000000.svg)](https://github.com/psf/black)
 
 Command-line scripts to do things with Strava.