Upgrade rubocop

example/server/liquid_servlet.rb

@@ -1,23 +1,28 @@
+# frozen_string_literal: true
+
 class LiquidServlet < WEBrick::HTTPServlet::AbstractServlet
-  def do_GET(req, res)
+  def get(req, res)
     handle(:get, req, res)
   end
 
-  def do_POST(req, res)
+  def post(req, res)
     handle(:post, req, res)
   end
 
+  alias_method :do_GET, :get
+  alias_method :do_POST, :post
+
   private
 
-  def handle(type, req, res)
+  def handle(_type, req, res)
     @request = req
     @response = res
 
     @request.path_info =~ /(\w+)\z/
-    @action = $1 || 'index'
+    @action = Regexp.last_match(1) || 'index'
     @assigns = send(@action) if respond_to?(@action)
 
-    @response['Content-Type'] = "text/html"
+    @response['Content-Type'] = 'text/html'
     @response.status = 200
     @response.body = Liquid::Template.parse(read_template).render(@assigns, filters: [ProductsFilter])
   end