Maintenance: Update included version of Action Scheduler library to 3.7.1. There shouldn't be any major changes in this library, so this just keeps the plugin's dependency up to date.

[jonathanstegall]

What does this Pull Request do?

Action Scheduler has had several small releases. None of them seem significant enough to be risky, so it seems like a good idea to put them in.

How do I test this Pull Request?

• run the plugin, and any scheduled actions and make sure nothing goes wrong