Fix Array/Hash monitor not being initialized

Fixes several broken testcases in the Array and Hash specs.

Author: ivoanjo

lib/concurrent/thread_safe/util/array_hash_rbx.rb

@@ -14,6 +14,12 @@ def initialize(*args)
             _mon_initialize
             super
           end
+
+          def self.allocate
+            obj = super
+            obj.send(:_mon_initialize)
+            obj
+          end
         end
 
         klass.superclass.instance_methods(false).each do |method|