Merge RubyGems-2.7.5 from upstream.

	  Please see its details: http://blog.rubygems.org/2018/02/06/2.7.5-released.html

	test_gem_util.rb: fix broken test

	* test/rubygems/test_gem_util.rb: no guarantee that tmpdir is
	  always underneath the root directory at all.

	test_gem_commands_setup_command.rb: BUNDLER_VERS

	* test/rubygems/test_gem_commands_setup_command.rb: run bundled
	  gem command, instead of installed one.

	no need to set bundled bundler unless Gem::USE_BUNDLER_FOR_GEMDEPS


	revert r62302 and force to define the version constant


	Merge RubyGems 2.7.6 from upstream.

	  It fixed some security vulnerabilities.

	  http://blog.rubygems.org/2018/02/15/2.7.6-released.html

	fix regexp literal warning.

	test/rubygems/test_gem_server.rb: eliminate duplicated character class warning.
	[Bug #14481]

	Remove unnecessary `[]`s

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@62837 b2dd03c8-39d4-4d8f-98ff-823fe69b080e