Field definition for InterfaceType does not work with callback function

[ivome]

This is possibly related to #22. When I try to define the fields as a callback function for an InterfaceType, I get an error:

Argument 1 passed to GraphQL\Type\Definition\FieldDefinition::createMap() must be of the type array, object given, called in /Users/ivo/Documents/workspace/graphql-relay-php/vendor/webonyx/graphql-php/src/Type/Definition/InterfaceType.php on line 66 and defined

[vladar]

Managed to miss interface field definitions somehow. Thanks for catching!

Should be fixed in d37fb34