Adjust gemspec location of default gems

lib/open3/open3.gemspec

@@ -1,8 +1,10 @@
 # frozen_string_literal: true
 
 name = File.basename(__FILE__, ".gemspec")
-version = File.foreach(File.join(__dir__, "lib/open3/version.rb")) do |line|
+version = ["lib", Array.new(name.count("-")+1, "..").join("/")].find do |dir|
+  break File.foreach(File.join(__dir__, dir, "#{name.tr('-', '/')}.rb")) do |line|
     /^\s*VERSION\s*=\s*"(.*)"/ =~ line and break $1
+  end rescue nil
 end
 
 Gem::Specification.new do |spec|