Fix nokogiri version

Author: do-your-own-seo

Gemfile

@@ -17,7 +17,7 @@ gem "sass", "~>3.4"
 gem 'html-proofer', '~> 5.0', '>= 5.0.8'
 gem "kramdown", "~>2.3.1"
 gem "kramdown-parser-gfm", "1.1.0"
-gem "nokogiri", "2.0.5"
+gem "nokogiri", "1.15.6"
 # Currently used version of nokogiri requires ruby >=2.6.0"
 
 # If you have any other plugins, list them here: