validation: fix bug in maxDepth fragment spread logic (graph-gophers#492

)

Accepting value Json in parameter of request's body in custom Scalar (g…

…raph-gophers#467)

Accept JSON value in resolver args

Merge pull request graph-gophers#456 from savaki/master

errors.Errorf preserves original error similar to fmt.Error

Merge pull request graph-gophers#443 from eko/fix-369

Fixed duplicated __typename in response (fixes graph-gophers#369)