title: Gatsby Wordpress ACF Image fields are returning 'null'
body: <p>I have a GatsbyJS site consuming data from Wordpress via <code>gatsby-source-wordpress</code>. It was all running fine until yesterday, when my queries began to fail. I am using Advanced Custom Fields and can no longer query image fields, my query looks like this when im getting all posts with a post type of 'Project'...</p>
  
  <pre><code>allWordpressWpProject {
      edges {
          node {
              title
              slug
              path
              link
              acf {
                  project_banner_title
                  project_slider_image {
                      source_url
                      alt_text
                  }
                  project_navigation_image {
                      source_url
                      alt_text
                  }
                  project_banner_image {
                      source_url
                      alt_text
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>But all image fields now return <code>null</code>. When I run the query via Wordpress or manually hit the <code>wp-json</code> endpoint the image fields return as expected.</p>
  
  <p>Any ideas?</p>