Warning/error message when versionFunctions is false

[yaronya]

What are the steps to reproduce this issue?

1. set versionFunctions to false
2. Try setting canary deployments, you'll get the error as in 'null' values are not allowed in templates #38

What happens?

Generated CF stack is malformed. The alias is created with a FunctionVersion referencing a nullish version.

What were you expecting to happen?

Have some sort of validation that outputs that versionFunctions must not be false, otherwise there isn't much point in using this plugin I suppose.

Any logs, error output, etc?

Can see more info in #38

What versions of software are you using?

sls 2.40