title: gatsby-source-filesystem allDirectory how to exclude root directory
body: <p>I have <code>gatsby-source-filesystem</code> configured like:</p>
  <pre><code>module.exports = {
    /* Your site config here */
    plugins: [
      {
        resolve: `gatsby-source-filesystem`,
        options:{
          name: `dosbox`,
          path: `${__dirname}/src/dosbox/`,
        }
      },
    ],
  }
  </code></pre>
  <p>I want to query for subdirectories in the <code>dosbox</code> directory. I don't want to return a reference to the <code>dosbox</code> directory itself. I use the following query</p>
  <pre><code>query MyQuery {
    allDirectory(filter: {sourceInstanceName: {eq: &quot;dosbox&quot;}}) {
      edges {
        node {
          name
          dir
          modifiedTime
        }
      }
    }
  }
  </code></pre>
  <p>This returns the following result. That returns the undesired root <code>dosbox</code> directory.</p>
  <pre><code>{
    &quot;data&quot;: {
      &quot;allDirectory&quot;: {
        &quot;edges&quot;: [
          {
            &quot;node&quot;: {
              &quot;name&quot;: &quot;dosbox&quot;,
              &quot;dir&quot;: &quot;/Users/kevzettler/code/radlab/src&quot;,
              &quot;modifiedTime&quot;: &quot;2020-09-09T04:52:09.400Z&quot;
            }
          },
          {
            &quot;node&quot;: {
              &quot;name&quot;: &quot;DOOM&quot;,
              &quot;dir&quot;: &quot;/Users/kevzettler/code/radlab/src/dosbox&quot;,
              &quot;modifiedTime&quot;: &quot;2020-09-09T05:22:20.000Z&quot;
            }
          }
        ]
      }
    },
    &quot;extensions&quot;: {}
  }
  </code></pre>