🚨 New Python runtime environment in Heroku

[miss-islington]

There's a new Python runtime enviornment in Heroku. You might want to update the bot to use the new environment by editing the runtime.txt file.

See the changelog at https://devcenter.heroku.com/changelog-items/1722
Message:
New python runtimes Python 3.8.1, 3.7.6, 3.6.10 are now available on the platform.

Additionally, Pypy 2.7 and 3.6 version 7.2.0 are now also released to Beta on the platform.

For more information, see Python Supported Runtimes

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