fix: Gemfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-RUBY-WEBRICK-8068535

Gemfile

@@ -6,7 +6,7 @@ group :jekyll_plugins do
   gem 'jekyll-tagging'
   gem "jekyll-sitemap"
   gem "jekyll-pagebreak", "~> 0.9"
-  gem "webrick", "~> 1.8"
+  gem "webrick", "~> 1.8", ">= 1.8.2"
   gem 'wdm', '~> 0.2.0', :install_if => Gem.win_platform?
   gem 'jekyll-feed'
 end