Require action_dispatch fully

It uses autoload, so it's lazy-loaded. However there are missing some
internal requires so it will asks for more not-related `requires`
when requiring some files directly.

spec/integration_helper.rb

@@ -1,7 +1,6 @@
 require 'telegram/bot/rspec/integration'
 require 'action_controller'
 require 'action_dispatch'
-require 'action_dispatch/testing/integration'
 
 require 'rails'
 require 'telegram/bot/railtie'

spec/telegram/bot/middleware_spec.rb

@@ -20,7 +20,6 @@ RSpec.describe Telegram::Bot::Middleware do
     if ActionPack::VERSION::MAJOR < 5
       # Before Rails 5, params are parsed in middleware.
       # In Rails 5, they are parsed in Request#request_parameters.
-      require 'action_dispatch/middleware/params_parser'
       let(:instance) { ActionDispatch::ParamsParser.new(super()) }
     end
 

spec/telegram/bot/rspec/integration_spec.rb

@@ -1,7 +1,6 @@
 require 'telegram/bot/rspec/integration'
 require 'action_controller'
 require 'action_dispatch'
-require 'action_dispatch/testing/integration'
 
 RSpec.describe 'Integrations helper', :telegram_bot do
   include ActionDispatch::Integration::Runner