Nokogiri must be v1.13.0 or later for changes on #121

The changes on #121 depends on updates on Nokogiri v1.13.0.

Author: satoryu

docx.gemspec

@@ -13,7 +13,7 @@ Gem::Specification.new do |s|
   s.files       = Dir['README.md', 'LICENSE.md', 'lib/**/*.rb']
   s.required_ruby_version = '>= 2.5.0'
 
-  s.add_dependency 'nokogiri', '~> 1.12', '>= 1.12.5'
+  s.add_dependency 'nokogiri', '~> 1.13', '>= 1.13.0'
   s.add_dependency 'rubyzip',  '~> 2.0'
 
   s.add_development_dependency 'coveralls_reborn', '~> 0.21'