fix(deps): update gatsby monorepo

Author: renovate-bot

package.json

@@ -21,10 +21,10 @@
     "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing \""
   },
   "dependencies": {
-    "gatsby": "2.15.2",
-    "gatsby-image": "2.2.23",
-    "gatsby-plugin-google-analytics": "2.1.19",
-    "gatsby-plugin-sitemap": "2.2.16",
+    "gatsby": "3.5.0",
+    "gatsby-image": "3.5.0",
+    "gatsby-plugin-google-analytics": "3.5.0",
+    "gatsby-plugin-sitemap": "4.1.0",
     "gatsby-theme-mdx-deck": "3.1.0",
     "gatsby-transformer-cloudinary": "0.3.5",
     "react": "16.13.1",