chore: add webrick since it's unbundled in Ruby 3.0.0

Author: ElMassimo

Gemfile

@@ -1,4 +1,8 @@
 source "https://rubygems.org"
+
+# Required in Ruby 3.0.0 as it's an unbundled gem now.
+gem "webrick"
+
 # Hello! This is where you manage which Jekyll version is used to run.
 # When you want to use a different version, change it below, save the
 # file and run `bundle install`. Run Jekyll with `bundle exec`, like so:

Gemfile.lock

@@ -64,6 +64,7 @@ GEM
     terminal-table (2.0.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     unicode-display_width (1.8.0)
+    webrick (1.7.0)
 
 PLATFORMS
   x86_64-darwin-19
@@ -75,6 +76,7 @@ DEPENDENCIES
   tzinfo (~> 1.2)
   tzinfo-data
   wdm (~> 0.1.1)
+  webrick
 
 BUNDLED WITH
    2.2.11