Merged r22102 from trunk to 4.2-stable (#38272).

git-svn-id: https://svn.redmine.org/redmine/branches/4.2-stable@22104 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -22,7 +22,7 @@ gem 'nokogiri', (if Gem.ruby_version < Gem::Version.new('2.5.0')
                    '~> 1.13.10'
                  end)
 gem 'i18n', '~> 1.8.2'
-gem "rbpdf", "~> 1.20.0"
+gem 'rbpdf', '~> 1.21.0'
 gem 'addressable'
 gem 'rubyzip', '~> 2.3.0'
 gem 'psych', '~> 3.1' if Gem.ruby_version < Gem::Version.new('2.6.0')