'Attachment model missing type definition for' errors

[jgedarovich]

While testing out this library I ran into the same problems as described in #59 . However, after applying the patch from #59 locally I found that It required further modifications, the full list of additions to CL.Slack.Model.Attachment.yml that worked for me was:

        mrkdwnIn:
            type: array
        titleLink:
            type: string
        authorName:
            type: string
        authorLink:
            type: string
        authorIcon:
            type: string

PR to follow.