Use require_relative for internal requires

lib/optparse/ac.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require 'optparse'
+require_relative '../optparse'
 
 class OptionParser::AC < OptionParser
   private

lib/optparse/date.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require 'optparse'
+require_relative '../optparse'
 require 'date'
 
 OptionParser.accept(DateTime) do |s,|

lib/optparse/kwargs.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
-require 'optparse'
+require_relative '../optparse'
 
 class OptionParser
   # :call-seq:

lib/optparse/shellwords.rb

@@ -2,6 +2,6 @@
 # -*- ruby -*-
 
 require 'shellwords'
-require 'optparse'
+require_relative '../optparse'
 
 OptionParser.accept(Shellwords) {|s,| Shellwords.shellwords(s)}

lib/optparse/time.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require 'optparse'
+require_relative '../optparse'
 require 'time'
 
 OptionParser.accept(Time) do |s,|

lib/optparse/uri.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 # -*- ruby -*-
 
-require 'optparse'
+require_relative '../optparse'
 require 'uri'
 
 OptionParser.accept(URI) {|s,| URI.parse(s) if s}