Fails to parse directives with no arguments

[Dig-Doug]

Fails to parse this:

directive @id on FIELD_DEFINITION

I get an error:

Invalid GraphQL: Expected https://facebook.github.io/graphql/June2018/#DirectiveDefinition
	line: 1 column: 14

Relevant GraphQL Spec: http://spec.graphql.org/June2018/#example-060af

[wravery]

It's not accepting an empty argument list for directive definitions.