chore(deps): update dependency gatsby-source-graphcms to v2.8.0

Author: renovate[bot]

package.json

@@ -22,7 +22,7 @@
     "gatsby-plugin-react-helmet": "3.3.13",
     "gatsby-plugin-react-svg": "3.0.0",
     "gatsby-plugin-sharp": "2.6.39",
-    "gatsby-source-graphcms": "2.0.0-next.11",
+    "gatsby-source-graphcms": "2.8.0",
     "gatsby-transformer-sharp": "2.5.17",
     "react": "16.13.1",
     "react-dom": "16.13.1",