title: Field "thumbnail" must not have a selection since type "String" has no subfields
body: <p>I have the following error with gatsbyJS : Field &quot;thumbnail&quot; must not have a selection since type &quot;String&quot; has no subfields.</p>
  <p>I already tryied to change the order of my plugin in my gatsby config file. When i go to : <a href="http://127.0.0.1:8000/__graphql" rel="nofollow noreferrer">http://127.0.0.1:8000/__graphql</a> and do this:</p>
  <pre><code>  query {
      profilePicture: file(absolutePath: { regex: &quot;img/profile_picture.png/&quot; })
      logoCreditAgricole: file(absolutePath: { regex: &quot;img/logo-credit-agricole.png/&quot; })
      site {
        siteMetadata {
          author
          social {
            twitter
          }
        }
      }
      allMarkdownRemark(
        sort: { fields: [frontmatter___date], order: DESC }
        filter: { frontmatter: { template: { eq: &quot;project&quot; } } }
        ) {
        edges{
          node{
            excerpt
            fields{
              slug
            }
            frontmatter{
              date(formatString: &quot;MMMM DD, YYYY&quot;)
              title
              thumbnail
            }
          }
        }
      }
    }
  </code></pre>
  <p>I have to remove</p>
  <pre><code>      childImageSharp {
          fluid(maxWidth: 100) {
            ...GatsbyImageSharpFluid
          }
        }
  </code></pre>
  <p>to make it work</p>
  <p>Here is my page query:</p>
  <pre><code>export const pageQuery = graphql`
    query {
      profilePicture: file(absolutePath: { regex: &quot;img/profile_picture.png/&quot; }) {
        childImageSharp {
          fluid(maxWidth: 700) {
            ...GatsbyImageSharpFluid
          }
        }
      }
      logoCreditAgricole: file(absolutePath: { regex: &quot;img/logo-credit-agricole.png/&quot; }) {
        childImageSharp {
          fluid(maxWidth: 100) {
            ...GatsbyImageSharpFluid
          }
        }
      }
      site {
        siteMetadata {
          author
          social {
            twitter
          }
        }
      }
      allMarkdownRemark(
        sort: { fields: [frontmatter___date], order: DESC }
        filter: { frontmatter: { template: { eq: &quot;project&quot; } } }
        ) {
        edges{
          node{
            excerpt
            fields{
              slug
            }
            frontmatter{
              date(formatString: &quot;MMMM DD, YYYY&quot;)
              title
              thumbnail {
                childImageSharp {
                  fluid(maxWidth: 700) {
                    ...GatsbyImageSharpFluid
                  }
                }
              }
            }
          }
        }
      }
    }
  `
  </code></pre>
  <p>My gatsbyconfig :</p>
  <pre><code>module.exports = {
    siteMetadata: {
      title: `Florent Vandroy`,
      author: `Florent Vandroy`,
      description: `Développeur web indépendant dans le secteur de Bergerac. Disponible pour la création ou modification de votre site web.`,
      siteUrl: `http://127.0.0.1:8000/`,
      social: {
        twitter: `alisalahio`,
      },
      projects: [
        {
          title: `Gatsby Starter Blog &amp; Portfolio!`,
          description: `Gatsby official starter with portfolio section added!`,
          url: `https://gatsby-starter-blog-and-portfolio.netlify.com/`,
          moreLinks: [
            {
              type: `Github`,
              url: `https://github.com/alisalahio/gatsby-starter-blog-and-portfolio`,
            },
          ],
        },
        {
          title: `React`,
          description: `React's homepage is created with Gatsby!`,
          url: `https://reactjs.org/`,
        },
      ],
    },
    plugins: [
      `gatsby-plugin-sharp`,
      `gatsby-transformer-sharp`,
      {
        resolve: `gatsby-transformer-remark`,
        options: {
          plugins: [
            {
              resolve: `gatsby-remark-images`,
              options: {
                maxWidth: 590,
              },
            },
            {
              resolve: `gatsby-remark-responsive-iframe`,
              options: {
                wrapperStyle: `margin-bottom: 1.0725rem`,
              },
            },
            `gatsby-remark-prismjs`,
            `gatsby-remark-copy-linked-files`,
            `gatsby-remark-smartypants`,
          ],
        },
      },    
      {
        resolve: `gatsby-source-filesystem`,
        options: {
          path: `${__dirname}/content/blog`,
          name: `blog`,
        },
      },
      {
        resolve: `gatsby-source-filesystem`,
        options: {
          path: `${__dirname}/content/project`,
          name: `project`,
        },
      },
      {
        resolve: `gatsby-source-filesystem`,
        options: {
          path: `${__dirname}/content/assets`,
          name: `assets`,
        },
      },
      {
        resolve: `gatsby-plugin-google-analytics`,
        options: {
          //trackingId: `ADD YOUR TRACKING ID HERE`,
        },
      },
      `gatsby-plugin-feed`,
      {
        resolve: `gatsby-plugin-manifest`,
        options: {
          name: `Gatsby Starter Blog`,
          short_name: `GatsbyJS`,
          start_url: `/`,
          background_color: `#ffffff`,
          theme_color: `#663399`,
          display: `minimal-ui`,
          icon: `content/assets/gatsby-icon.png`,
        },
      },
      `gatsby-plugin-offline`,
      `gatsby-plugin-react-helmet`,
      {
        resolve: `gatsby-plugin-typography`,
        options: {
          pathToConfigModule: `src/utils/typography`,
        },
      },
      `gatsby-plugin-sass`
    ],
  }
  
  </code></pre>
  <p>my index.md file inside /content/project/index.md :</p>
  <pre><code>---
  title: Hello World
  date: &quot;2015-05-01T22:12:03.284Z&quot;
  template: &quot;project&quot;
  thumbnail: &quot;/cashprono.png&quot;
  ---
  </code></pre>
  <p>Thank to all who will try to help me.</p>