Support ".ruby-version" as fallback for Ruby version

[FranklinYu]

Currently if Ruby version is not specified in Gemfile, it fallback to default version (2.3.4 currently). See this Gist for description of .ruby-version file. Currently my .ruby-version looks like ruby-2.4.1.

I think this method is related.

[schneems]

This isn't the place for that functionality. We get our Ruby version from Bundler. The best way to do it would have bundle update --ruby also generate a .ruby-version that you can use locally. Or alternatively have ruby version managers that do switching read in the version from Gemfile.lock, actually that would be better.

That being said you can build this yourself with:

# Gemfile
ruby File.read(".ruby-version")