Should it be an error instead of a warning when a dependency doesn't support the target Elm version?

[avh4]

For example, a project upgrade shows:

WARNING: rtfeldman/elm-validate has not been upgraded to 0.18 yet!

But then also indicates success at the end. Should this instead be a fatal error for the upgrade?

cc @eeue56

[eeue56]

It should definitely not be a fatal error - but maybe it should log it as an error.

The reasoning being, if you can upgrade 90% of the deps, that's great. Then you want to handle the package that isn't upgraded yet somehow. Maybe we can add a link so they can make a PR or something.

[avh4]

Maybe slightly change the message to something like "The author of rtfeldman/elm-validate hasn't yet published a version that's compatible with Elm 0.18" to sort of hint at what needs to be done

[avh4]

Closed via #5