rails_version_specifier

# File railties/lib/rails/generators/app_base.rb, line 483
      def rails_version_specifier(gem_version = Rails.gem_version)
        if gem_version.segments.size == 3 || gem_version.release.segments.size == 3
          # ~> 1.2.3
          # ~> 1.2.3.pre4
          "~> #{gem_version}"
        else
          # ~> 1.2.3, >= 1.2.3.4
          # ~> 1.2.3, >= 1.2.3.4.pre5
          patch = gem_version.segments[0, 3].join(".")
          ["~> #{patch}", ">= #{gem_version}"]
        end
      end