Merge branch 'fix-jekyll-serve-3.0' into 'master'

Fix jekyll serve failing with Ruby 3.0

See merge request !297

Gemfile

@@ -8,6 +8,7 @@ gem 'rouge', '~> 3.26.0'
 gem 'jekyll-redirect-from', '~> 0.16.0'
 gem 'jekyll-feed', '~> 0.15.1'
 gem "jekyll-sitemap", "~> 1.4"
+gem "webrick", "~> 1.7"
 
 group :test do
     gem 'html-proofer', '~> 3.19.2'

Gemfile.lock

@@ -84,6 +84,7 @@ GEM
     typhoeus (1.4.0)
       ethon (>= 0.9.0)
     unicode-display_width (1.7.0)
+    webrick (1.7.0)
     yaml-lint (0.0.10)
     yell (2.2.2)
 
@@ -98,7 +99,8 @@ DEPENDENCIES
   jekyll-redirect-from (~> 0.16.0)
   jekyll-sitemap (~> 1.4)
   rouge (~> 3.26.0)
+  webrick (~> 1.7)
   yaml-lint (~> 0.0.7)
 
 BUNDLED WITH
-   2.1.4
+   2.2.22