title: Trouble returning Prismic slices with gatsby-source-prismic
body: <p>I'm using the localhost:8000/___graphq debugger and <a href="https://www.gatsbyjs.org/packages/gatsby-source-prismic/?=prismic#query-slices" rel="nofollow noreferrer">gatsby-source-prismic</a> to returning my slices from  prismic cms. I followed the steps in the readme and I get the correct typenames with this snippet: </p>
  
  <pre><code>{
    prismicHomepage {
      data {
        body {
          __typename
        }
      }
    }
  }
  </code></pre>
  
  <p>My problem is to create the inline fragment:</p>
  
  <pre><code>{
    prismicHomepage {
      data {
        body {
          __typename
          ... on PrismicHomepageBodyText {
            text {
              html
            }
          }
        }
      }
    }
  }
  </code></pre>
  
  <p>After this I get the error:</p>
  
  <pre><code>{
    "errors": [
      {
        "message": "Cannot query field \"text\" on type \"PrismicHomepageBodyText\".",
        "locations": [
          {
            "line": 10,
            "column": 11
          }
        ]
      }
    ]
  }
  </code></pre>
  
  <p>My slices has the API ID : text and I created an single site filled with this slices.</p>
  
  <p>I have no problem to fetch any other API ID, so what did I forget?</p>