Support null-prototype mutation payload objects
Support null-prototype mutation payload objects

Summary:This came to my attention via https://github.com/relay-tools/relay-local-schema/pull/15. Recent versions of graphql-js use `null`-prototype objects for maps, which leads to the `payload.hasOwnProperty` call below failing when directly feeding the output of in-process graphql-js into Relay (e.g. with relay-local-schema).

I felt that it was trivial enough to just make this little patch here.
Closes https://github.com/facebook/relay/pull/972

Reviewed By: josephsavona

Differential Revision: D3082405

Pulled By: wincent

fb-gh-sync-id: cb0c5fa72792a514165fc08e90bc7d5b60f684ce
shipit-source-id: cb0c5fa72792a514165fc08e90bc7d5b60f684ce

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