Error serializing requests with extensions (Apollo client 2.0)

[ronald-d-rogers]

The 2.0 version of apollo client's GraphQL requests can contain the property extensions which causes it to fail to deserialize to GraphQLServlet$GraphQLRequest because it is not also defined there.

I guess the best thing to do would be to simply ignore any unknown JSON properties.

I will go ahead and create a PR for it.

[oliemansm]

Closing since already fixed