Describe the bug

Looking at the 2018 GraphQL spec, it has for a while allowed for an optional leading | in directive locations. E.g., the following is valid GraphQL:

directive @foo on
    | OBJECT
    | INTERFACE

However, trying to parse this with graphql-java throws, because the ANTLR grammar doesn't allow the optional leading |.

To Reproduce

This code snippet throws:

new SchemaParser().parse("directive @foo on | OBJECT");