Add test for false value

[ghost]

Addition of a test for false value and small modification of test for nil value

  test "nil value" do
    json = Jbuilder.encode do |json|
      json.content nil
    end

    JSON.parse(json).tap do |parsed|
      assert parsed.has_key?("content")
      assert_equal nil, parsed["content"]
    end
  end

  test "false value" do
    json = Jbuilder.encode do |json|
      json.published false
    end

    assert_equal false, JSON.parse(json)["published"]
  end

[joshmcarthur]

Thanks for improving our tests @delba!
I've merged this into master, so it should be lodged against the pull request I've opened against the main repository to fix the issue at rails#15