Only deploy when certain files change

[barrettj12]

Some of the files in the repo won't affect the Fly image. Hence, we don't need to trigger a new deploy for these.

Include:

• src/**.go
• main.go
• favicon.ico
• fly.toml
• go.mod
• go.sum ???

Ignore:

• .github/**
• docs/**
• src/cmd/**
• src/**_test.go ***note below
• tests/** ***note below
• .gitignore
• **.md

*** possible issue if the tests fail, blocking a deploy, then we fix the tests, which should allow the deploy to go through. Worst case we can always deploy manually though.

[barrettj12]

Maybe we could check the SHA of the built Fly image (or the built Go binary), and only do a deploy if that has changed.