fix(deps): move html-proofer to test group

Resolves nokogiri compilation errors in Cloudflare Pages by excluding html-proofer from production builds

Author: johnsBeharry

Gemfile

@@ -18,6 +18,9 @@ group :jekyll_plugins do
   gem "jekyll-feed", "~> 0.12"
   gem "jekyll-seo-tag"
   gem 'jekyll-compress-images', :git => 'https://github.com/valerijaspasojevic/jekyll-compress-images.git'
+end
+
+group :test do
   gem 'html-proofer'
 end