Adding some specs for #as_json on ObjectSerializer class.

[corinnekunze]

Added some tests here to ensure that we are maintaining availability of the as_json method on our Object Serializer.

Allowing as_json to successfully parse a json hash on the serializer was added in this pull request:
#89

I added a director attr_accessor in the movie context that acts to prove if an attribute is present on the record but not defined in the serializer, it should not be returned.

[shishirmk]

Thank you for adding the tests

[corinnekunze]

You bet!