make ruby version optional in Gemfile

Gemfile

@@ -7,7 +7,7 @@
 
 # defaults that may be modified in Gemfile.conf
 $source        = "https://rubygems.org"
-$ruby_version  = "3.1.1"
+$ruby_version  = nil
 $javascript    = true
 $gemfile_first = File.expand_path('../Gemfile.first', __FILE__)
 $gemfile_last  = File.expand_path('../Gemfile.last', __FILE__)
@@ -17,7 +17,7 @@ if File.exist?($gemfile_first)
 end
 
 source $source
-ruby $ruby_version
+ruby $ruby_version if $ruby_version
 
 ##
 ## DEFAULT CORE RAILS