Bump nokogiri to 1.8.4 and sanitize to 4.6.6 for performance

sanitize 4.6.6 has this optimization that will benefit Markdown rendering: https://github.com/rgrove/sanitize/pull/183

nokogiri 1.4.4 has this memory leak fix: https://github.com/sparklemotion/nokogiri/pull/1771

Gemfile

@@ -233,7 +233,7 @@ gem 'ruby-fogbugz', '~> 0.2.1'
 gem 'kubeclient', '~> 3.1.0'
 # Sanitize user input
-gem 'sanitize', '~> 4.6.5'
+gem 'sanitize', '~> 4.6'
 gem 'babosa', '~> 1.0.2'
 # Sanitizes SVG input

Gemfile.lock

@@ -514,7 +514,7 @@ GEM
     net-ldap (0.16.0)
     net-ssh (5.0.1)
     netrc (0.11.0)
-    nokogiri (1.8.3)
+    nokogiri (1.8.4)
       mini_portile2 (~> 2.3.0)
     nokogumbo (1.5.0)
       nokogiri
@@ -808,7 +808,7 @@ GEM
       et-orbi (~> 1.0)
     rugged (0.27.2)
     safe_yaml (1.0.4)
-    sanitize (4.6.5)
+    sanitize (4.6.6)
       crass (~> 1.0.2)
       nokogiri (>= 1.4.4)
       nokogumbo (~> 1.4)
@@ -1157,7 +1157,7 @@ DEPENDENCIES
   ruby_parser (~> 3.8)
   rufus-scheduler (~> 3.4)
   rugged (~> 0.27)
-  sanitize (~> 4.6.5)
+  sanitize (~> 4.6)
   sass-rails (~> 5.0.6)
   scss_lint (~> 0.56.0)
   seed-fu (~> 2.3.7)

Gemfile.rails5.lock

@@ -1168,7 +1168,7 @@ DEPENDENCIES
   ruby_parser (~> 3.8)
   rufus-scheduler (~> 3.4)
   rugged (~> 0.27)
-  sanitize (~> 4.6.5)
+  sanitize (~> 4.6)
   sass-rails (~> 5.0.6)
   scss_lint (~> 0.56.0)
   seed-fu (~> 2.3.7)

changelogs/unreleased/sh-bump-sanitize-4-6-6.yml

+---
+title: Bump nokogiri to 1.8.4 and sanitize to 4.6.6 for performance
+merge_request: 20795
+author:
+type: performance