Use correct Nokogiri versions for different Ruby versions

Author: Juanito Fatas

Gemfile

@@ -3,5 +3,15 @@ source 'https://rubygems.org'
 # Specify your gem's dependencies in html-sanitizer.gemspec
 gemspec
 
-gem "nokogiri", RUBY_VERSION < "2.1" ? "~> 1.6.0" : ">= 1.7"
+nokogiri_version = case
+  when RUBY_VERSION < "2.1"
+    "~> 1.6.0"
+  when RUBY_VERSION < "2.3"
+    "~> 1.9.1"
+  else
+    ">= 1.10.0"
+  end
+end
+
+gem "nokogiri", nokogiri_version
 gem "activesupport", RUBY_VERSION < "2.2.2" ? "~> 4.2.0" : ">= 5"