[rubygems/rubygems] Lazy require stringio

https://github.com/rubygems/rubygems/commit/82f0d4ca69

lib/rubygems/mock_gem_ui.rb

@@ -1,5 +1,4 @@
 # frozen_string_literal: true
-require 'stringio'
 require 'rubygems/user_interaction'
 
 ##
@@ -46,6 +45,7 @@ class Gem::MockGemUi < Gem::StreamUI
   end
 
   def initialize(input = "")
+    require 'stringio'
     ins = StringIO.new input
     outs = StringIO.new
     errs = StringIO.new

lib/rubygems/specification.rb

@@ -14,7 +14,6 @@ require 'rubygems/basic_specification'
 require 'rubygems/stub_specification'
 require 'rubygems/specification_policy'
 require 'rubygems/util/list'
-require 'stringio'
 
 ##
 # The Specification class contains the information for a gem.  Typically
@@ -2535,6 +2534,7 @@ class Gem::Specification < Gem::BasicSpecification
     builder << self
     ast = builder.tree
 
+    require 'stringio'
     io = StringIO.new
     io.set_encoding Encoding::UTF_8