Switch to a minimum of Python 3.7 due to dependency requirements

README.md

@@ -137,7 +137,7 @@ If your network requires connections to use an existing proxy, you can instruct
 After installing its requirements, the proxy script can be packaged as a single self-contained executable using [pyinstaller](https://pyinstaller.org/) if desired: `pyinstaller --onefile emailproxy.py`.
 If you are using the GUI version of the proxy, you may need to add `--hidden-import timeago.locales.en_short` until [this `timeago` issue](https://github.com/hustcc/timeago/issues/40) is resolved.
 
-Python 3.6 or later is required to run the proxy.
+Python 3.7 or later is required to run the proxy.
 The [python2 branch](https://github.com/simonrob/email-oauth2-proxy/tree/python2) provides minimal compatibility with python 2.7, but with a limited feature set, and no ongoing maintenance.
 See [issue 38](https://github.com/simonrob/email-oauth2-proxy/issues/38) for further discussion.
 

pyproject.toml

@@ -10,7 +10,7 @@ authors = [
 description = "Transparently add OAuth 2.0 support to IMAP/POP/SMTP clients that don't support this authentication method."
 readme = { file = "README.md", content-type = "text/markdown" }
 license = { text = "Apache License 2.0" }
-requires-python = ">=3.6"
+requires-python = ">=3.7"
 classifiers = [
     "Operating System :: OS Independent",
     "Operating System :: MacOS",