Add htmlproofer in Gemfile.lock

In 0317303, I've added `htmlproofer` to
`Gemfile`, but did not commit the changes to `Gemfile.lock`. This commit
adds it back.

Gemfile.lock

@@ -1,19 +1,44 @@
 GEM
  remote: https://rubygems.org/
  specs:
+ Ascii85 (1.1.0)
  addressable (2.8.0)
  public_suffix (>= 2.0.2, < 5.0)
+ afm (0.2.2)
+ async (2.6.4)
+ console (~> 1.10)
+ fiber-annotation
+ io-event (~> 1.1)
+ timers (~> 4.1)
  colorator (1.1.0)
  concurrent-ruby (1.1.10)
+ console (1.23.2)
+ fiber-annotation
+ fiber-local
  em-websocket (0.5.3)
  eventmachine (>= 0.12.9)
  http_parser.rb (~> 0)
+ ethon (0.16.0)
+ ffi (>= 1.15.0)
  eventmachine (1.2.7)
  ffi (1.15.5)
+ fiber-annotation (0.2.0)
+ fiber-local (1.0.0)
  forwardable-extended (2.6.0)
+ hashery (2.1.2)
+ html-proofer (5.0.8)
+ addressable (~> 2.3)
+ async (~> 2.1)
+ nokogiri (~> 1.13)
+ pdf-reader (~> 2.11)
+ rainbow (~> 3.0)
+ typhoeus (~> 1.3)
+ yell (~> 2.0)
+ zeitwerk (~> 2.5)
  http_parser.rb (0.8.0)
  i18n (1.10.0)
  concurrent-ruby (~> 1.0)
+ io-event (1.3.2)
  jekyll (4.2.2)
  addressable (~> 2.4)
  colorator (~> 1.0)
@@ -44,26 +69,44 @@ GEM
  rb-fsevent (~> 0.10, >= 0.10.3)
  rb-inotify (~> 0.9, >= 0.9.10)
  mercenary (0.4.0)
+ nokogiri (1.15.4-arm64-darwin)
+ racc (~> 1.4)
  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 (1.7.1)
+ rainbow (3.1.1)
  rb-fsevent (0.11.1)
  rb-inotify (0.10.1)
  ffi (~> 1.0)
  rexml (3.2.5)
  rouge (3.28.0)
+ ruby-rc4 (0.1.5)
  safe_yaml (1.0.5)
  sassc (2.4.0)
  ffi (~> 1.9)
  terminal-table (2.0.0)
  unicode-display_width (~> 1.1, >= 1.1.1)
+ timers (4.3.5)
+ ttfunk (1.7.0)
+ typhoeus (1.4.0)
+ ethon (>= 0.9.0)
  unicode-display_width (1.8.0)
  webrick (1.7.0)
+ yell (2.2.2)
+ zeitwerk (2.6.11)
 
 PLATFORMS
  ruby
 
 DEPENDENCIES
+ html-proofer
  jekyll (~> 4.2.1)
  jekyll-redirect-from
  webrick (~> 1.7)