Merge RubyGems 2.7.7

see release details here: https://blog.rubygems.org/2018/05/18/2.7.7-released.html

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63461 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/commands/push_command.rb

@@ -13,7 +13,7 @@ class Gem::Commands::PushCommand < Gem::Command
 The push command uploads a gem to the push server (the default is
 https://rubygems.org) and adds it to the index.
 
-The gem can be removed from the index (but only the index) using the yank
+The gem can be removed from the index and deleted from the server using the yank
 command.  For further discussion see the help for the yank command.
     EOF
   end

lib/rubygems/commands/setup_command.rb

@@ -385,7 +385,7 @@ By default, this RubyGems will install gem as:
         each {|default_gem| rm_r File.join(bundler_spec.gems_dir, default_gem) }
     end
 
-    bundler_bin_dir = File.join(Gem.default_dir, 'gems', bundler_spec.full_name, bundler_spec.bindir)
+    bundler_bin_dir = bundler_spec.bin_dir
     bundler_bin_dir = File.join(options[:destdir], bundler_bin_dir) unless Gem.win_platform?
     mkdir_p bundler_bin_dir
     bundler_spec.executables.each do |e|

lib/rubygems/commands/unpack_command.rb

@@ -183,7 +183,7 @@ command help for an example.
         when 'metadata' then
           metadata = entry.read
         when 'metadata.gz' then
-          metadata = Gem.gunzip entry.read
+          metadata = Gem::Util.gunzip entry.read
         end
       end
     end