diff --git a/Gemfile b/Gemfile
index f3a5b7d6..27a882f2 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,4 +9,4 @@ gem 'wdm', '>= 0.1.1' if Gem.win_platform?
 
 gem "webrick", "~> 1.7"
 
-gem 'html-proofer', "~> 3.19.4"
+gem 'html-proofer', "~> 5.0.4"
diff --git a/Gemfile.lock b/Gemfile.lock
index 991347ee..0a34c6fe 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,14 +1,20 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    Ascii85 (1.1.0)
     activesupport (6.0.5.1)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
       zeitwerk (~> 2.2, >= 2.2.2)
-    addressable (2.8.0)
-      public_suffix (>= 2.0.2, < 5.0)
+    addressable (2.8.1)
+      public_suffix (>= 2.0.2, < 6.0)
+    afm (0.2.2)
+    async (2.3.1)
+      console (~> 1.10)
+      io-event (~> 1.1)
+      timers (~> 4.1)
     coffee-script (2.4.1)
       coffee-script-source
       execjs
@@ -16,12 +22,14 @@ GEM
     colorator (1.1.0)
     commonmarker (0.23.5)
     concurrent-ruby (1.1.10)
+    console (1.16.2)
+      fiber-local
     dnsruby (1.61.9)
       simpleidn (~> 0.1)
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
-    ethon (0.15.0)
+    ethon (0.16.0)
       ffi (>= 1.15.0)
     eventmachine (1.2.7)
     eventmachine (1.2.7-x64-mingw32)
@@ -32,6 +40,7 @@ GEM
     faraday-net_http (2.0.3)
     ffi (1.15.5)
     ffi (1.15.5-x64-mingw32)
+    fiber-local (1.0.0)
     forwardable-extended (2.6.0)
     gemoji (3.0.1)
     github-pages (227)
@@ -85,20 +94,23 @@ GEM
       octokit (~> 4.0)
       public_suffix (>= 3.0, < 5.0)
       typhoeus (~> 1.3)
+    hashery (2.1.2)
     html-pipeline (2.14.2)
       activesupport (>= 2)
       nokogiri (>= 1.4)
-    html-proofer (3.19.4)
+    html-proofer (5.0.4)
       addressable (~> 2.3)
-      mercenary (~> 0.3)
+      async (~> 2.1)
       nokogiri (~> 1.13)
-      parallel (~> 1.10)
+      pdf-reader (~> 2.11)
       rainbow (~> 3.0)
       typhoeus (~> 1.3)
       yell (~> 2.0)
+      zeitwerk (~> 2.5)
     http_parser.rb (0.8.0)
     i18n (0.9.5)
       concurrent-ruby (~> 1.0)
+    io-event (1.1.6)
     jekyll (3.9.2)
       addressable (~> 2.4)
       colorator (~> 1.0)
@@ -216,31 +228,35 @@ GEM
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.3.6)
-    mini_portile2 (2.8.0)
+    mini_portile2 (2.8.1)
     minima (2.5.1)
       jekyll (>= 3.5, < 5.0)
       jekyll-feed (~> 0.9)
       jekyll-seo-tag (~> 2.1)
     minitest (5.16.2)
-    nokogiri (1.13.7)
+    nokogiri (1.14.0)
       mini_portile2 (~> 2.8.0)
       racc (~> 1.4)
-    nokogiri (1.13.7-x64-mingw32)
-      racc (~> 1.4)
     octokit (4.25.1)
       faraday (>= 1, < 3)
       sawyer (~> 0.9)
-    parallel (1.22.1)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
+    pdf-reader (2.11.0)
+      Ascii85 (~> 1.0)
+      afm (~> 0.2.1)
+      hashery (~> 2.0)
+      ruby-rc4
+      ttfunk
     public_suffix (4.0.7)
-    racc (1.6.0)
+    racc (1.6.2)
     rainbow (3.1.1)
     rb-fsevent (0.11.1)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rexml (3.2.5)
     rouge (3.26.0)
+    ruby-rc4 (0.1.5)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)
     safe_yaml (1.0.5)
@@ -257,6 +273,8 @@ GEM
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     thread_safe (0.3.6)
+    timers (4.3.5)
+    ttfunk (1.7.0)
     typhoeus (1.4.0)
       ethon (>= 0.9.0)
     tzinfo (1.2.9)
@@ -264,7 +282,6 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.8.2)
-    unf_ext (0.0.8.2-x64-mingw32)
     unicode-display_width (1.8.0)
     webrick (1.7.0)
     yell (2.2.2)
@@ -276,7 +293,7 @@ PLATFORMS
 
 DEPENDENCIES
   github-pages (= 227)
-  html-proofer (~> 3.19.4)
+  html-proofer (~> 5.0.4)
   webrick (~> 1.7)
 
 BUNDLED WITH