goenv: Read version from go.mod if .go-version is not available

Tracking version in .go-version is useful for scenarios where the user of goenv (who has goenv installed locally) is also a maintainer, or simply when the project has .go-version.

It would be great if goenv could also adapt to a scenario where project does not have .go-version for any reason, but the version can be read from go.mod file (go directive specifically):

module my-module

go 1.11

With that in mind, assuming that the version listed in go.mod is installed and there’s no .go-version, goenv could behave the same way as if there is .go-version and just switch to the relevant compatible Go version.

It’s worth noting that the two are not equivalent since go.mod only tracks minor versions (not patch versions), but I assume that goenv could just pick the latest compatible patch version that is installed?