[Schema Inaccuracy] schema `content-directory` should have enum limited to `dir` value in gh-3.18

[davidmoten]

Schema Inaccuracy

In the latest version of gh.yaml (3.18) the type content-directory has an incorrect type property.

    content-directory:
      title: Content Directory
      description: A list of directory items
      type: array
      items:
        type: object
        properties:
          type:
            type: string
            enum:
            - dir
            - file
            - submodule
            - symlink
...

Expected

    content-directory:
      title: Content Directory
      description: A list of directory items
      type: array
      items:
        type: object
        properties:
          type:
            type: string
            enum:
            - dir
...