Explicitly install webrick for Ruby 3.x

Gemfile

@@ -2,6 +2,7 @@ source 'https://rubygems.org'
 
 group :development, :test do
   gem 'rspec', '~> 3.8.0'
+  gem 'webrick', '~> 1.7'
 end
 
 group :development, :danger do

Gemfile.lock

@@ -104,6 +104,7 @@ GEM
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     unicode-display_width (2.2.0)
+    webrick (1.7.0)
 
 PLATFORMS
   ruby
@@ -111,6 +112,7 @@ PLATFORMS
 DEPENDENCIES
   gitlab-dangerfiles (~> 3.5.1)
   rspec (~> 3.8.0)
+  webrick (~> 1.7)
 
 BUNDLED WITH
    2.3.15