Update gemfile

remove unnecessary gems
guard dev-only gems behind condition

Gemfile

@@ -1,16 +1,13 @@
-# frozen_string_literal: true
-
 source "https://rubygems.org"
 
-git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
-
-gem "jekyll"
-gem "jekyll-theme-cayman"
-
-# gem "rails"
-
-gem "webrick", "~> 1.8"
 gem "github-pages", group: :jekyll_plugins
 
-# required on Windows to avoid polling for changes
-gem 'wdm', '>= 0.1.0' if Gem.win_platform?
+install_if -> { ENV["JEKYLL_ENV"] != "production" } do
+    puts "non-prod environment detected - installing webrick HTTP server for local debugging"
+    gem "webrick", "~> 1.8"
+
+    install_if Gem.win_platform? do
+        puts "Windows plaform detected - installing Windows Directory Monitor (Performance-booster)"
+        gem "wdm", "~> 0.1.0"
+    end
+end