Fix missing documentation coverage.

Author: ioquatix

lib/async/limited_queue.rb

@@ -8,8 +8,6 @@
 
 module Async
 	class LimitedQueue < Queue
-		class << self
-			remove_method :new
-		end
+		singleton_class.remove_method(:new)
 	end
 end

lib/async/queue.rb

@@ -133,6 +133,7 @@ def wait
 	# A queue which limits the number of items that can be enqueued.
 	# @public Since *Async v1*.
 	class LimitedQueue < Queue
+		# @private This exists purely for emitting a warning.
 		def self.new(...)
 			warn("`require 'async/limited_queue'` to use `Async::LimitedQueue`.", uplevel: 1, category: :deprecated) if $VERBOSE