Use `require` instead of `autoload` for fourflusher

Fixes #5445

lib/cocoapods/validator.rb

 require 'active_support/core_ext/array'
 require 'active_support/core_ext/string/inflections'
 
-autoload :Fourflusher, 'fourflusher'
-
 module Pod
   # Validates a Specification.
   #
@@ -719,6 +717,7 @@ module Pod
     #         returns its output (both STDOUT and STDERR).
     #
     def xcodebuild
+      require 'fourflusher'
       command = %w(clean build -workspace App.xcworkspace -scheme App -configuration Release)
       case consumer.platform_name
       when :ios

spec/unit/validator_spec.rb

@@ -392,6 +392,7 @@ module Pod
       end
 
       it 'checks if xcodebuild returns a successful status code' do
+        require 'fourflusher'
         Fourflusher::SimControl.any_instance.stubs(:destination).returns(['-destination', 'id=XXX'])
         Validator.any_instance.unstub(:xcodebuild)
         validator = Validator.new(podspec_path, config.sources_manager.master.map(&:url))
@@ -411,6 +412,7 @@ module Pod
       end
 
       it 'runs xcodebuild with correct arguments for code signing' do
+        require 'fourflusher'
         Fourflusher::SimControl.any_instance.stubs(:destination).returns(['-destination', 'id=XXX'])
         Validator.any_instance.unstub(:xcodebuild)
         validator = Validator.new(podspec_path, config.sources_manager.master.map(&:url))