use rainbows instead of puma in examples

examples/chat.rb

@@ -1,7 +1,8 @@
 #!/usr/bin/env ruby -I ../lib -I lib
 # coding: utf-8
+require_relative 'rainbows'
 require 'sinatra'
-set :server, 'puma'
+set :server, :rainbows
 connections = []
 
 get '/' do

examples/rainbows.rb

@@ -0,0 +1,20 @@
+require 'rainbows'
+
+module Rack
+  module Handler
+    class Rainbows
+      def self.run(app, **options)
+        rainbows_options = {
+          listeners: ["#{options[:Host]}:#{options[:Port]}"],
+          worker_processes: 1,
+          timeout: 30,
+          config_file: ::File.expand_path('rainbows.conf', __dir__),
+        }
+
+        ::Rainbows::HttpServer.new(app, rainbows_options).start.join
+      end
+    end
+
+    register :rainbows, ::Rack::Handler::Rainbows
+  end
+end

test/integration/rainbows.rb

@@ -8,13 +8,13 @@ module Rack
           listeners: ["#{options[:Host]}:#{options[:Port]}"],
           worker_processes: 1,
           timeout: 30,
-          config_file: ::File.expand_path('../rainbows.conf', __FILE__),
+          config_file: ::File.expand_path('rainbows.conf', __dir__),
         }
 
         ::Rainbows::HttpServer.new(app, rainbows_options).start.join
       end
     end
 
-    register "rainbows", "Rack::Handler::Rainbows"
+    register :rainbows, ::Rack::Handler::Rainbows
   end
 end