Support SQLAlchemy < 1.4 without a deprecation warning on 1.4+

[marcua]

Thanks for a great package! Here's a small tweak:

• A recent PR introduced backward-compatibility for SQLAlchemy < 1.4
• The replaced method is being deprecated and is causing deprecation warnings on newer versions of SQLAlchemy
• The docs suggest an easy way to keep backward-compatibility without receiving deprecation warnings in future versions
• This PR implements that suggestion
• Note: I wasn't sure how to run tests---if there's anything I should do beyond what I've already done, let me know. Perhaps GH Actions will run tests in your repo?

[Mause]

Many thanks for this!

[marcua]

Thank you so much @Mause!