AroundProxy should use an ExampleGroup instance

The example_block instance evaled in Example#run is instance evaled by a
ExampleGroup instance if no around eachs are given. We should do the same when
around eachs are given.

lib/rspec/core/example.rb

@@ -46,7 +46,7 @@ def run(example_group_instance, reporter)
             if @example_group_class.around_eachs.empty?
               @example_group_instance.instance_eval(&example_block) unless pending
             else
-              @example_group_class.around_eachs.first.call(AroundProxy.new(self, &example_block))
+              @example_group_class.around_eachs.first.call(AroundProxy.new(@example_group_instance, &example_block))
             end
             throw :pending_declared_in_example, false
           end