fly.io checks trigger heartbeat so machine never stops

[Mark Iannucci]

Thank you for your work on this. I was tinkering with getting this to work with fly.io's machines functionality so that way I could have my instance scale to 0 when I'm not using it. In attempting to get the machines to scale to 0, I noticed that the calls to the /check endpoint triggered the machinesHeartbeat function which kept the machine running which prevented the auto scaling from scaling it to 0.

I think I have a fix for this and will submit a PR momentarily.