* lib/rubygems.rb, lib/rubygems/*, test/rubygems/*: Update rubygems-2.5.2.

It supports to enable frozen string literal and add `--norc` option for
  disable to `.gemrc` configuration.
  See 2.5.2 release notes for other fixes and enhancements.
  a8aa3bac72/History.txt (L3)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53707 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/commands/environment_command.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require 'rubygems/command'
 
 class Gem::Commands::EnvironmentCommand < Gem::Command
@@ -72,7 +72,7 @@ lib/rubygems/defaults/operating_system.rb
   end
 
   def execute
-    out = ''
+    out = String.new
     arg = options[:args][0]
     out <<
       case arg
@@ -104,7 +104,7 @@ lib/rubygems/defaults/operating_system.rb
   end
 
   def show_environment # :nodoc:
-    out = "RubyGems Environment:\n"
+    out = "RubyGems Environment:\n".dup
 
     out << "  - RUBYGEMS VERSION: #{Gem::VERSION}\n"
 
@@ -158,4 +158,3 @@ lib/rubygems/defaults/operating_system.rb
   end
 
 end
-