Extend include_json to match elements inside an array of hash

Background:
Right now include_json can't test a specific element inside a hash that is included in an array. 
I understand that the package comes with exclude_keys, but it'd be handy if it can only match up the elements that I care about.

Use case
==============
Given actual (json object) and expected(hash):

JSON.parse(actual)
[{"user1" => {"name" => "Mike", "gender" => "male"}}, {"user2" => {"name" => "Abby", "gender" => "female"}}]

expected
{"name" => "Abby", "gender" => "female"}

actual.should include_json(expected.to_json)
> false

This patch will make the following truthy:

actual.should include_json(expected.to_json)
> true