Support a joined field in sqlDeps

[lorensr]

Querying for Post.description currently gives an error saying there's no such column posts.author (which is true—there's only an posts.author_id).

    Post: {
      sqlTable: 'posts',
      uniqueKey: 'id',
      fields: {
        author: {
          sqlJoin: (postTable, userTable) =>
            `${postTable}.author_id = ${userTable}.id`
        },
        title: { sqlColumn: 'title' },
        description: { sqlDeps: ['title', 'author'] },

Further, would be nice to be able to do sqlDeps: ['title', 'author.first_name', 'author.last_name']