Update dependency gatsby-plugin-offline to v3

Author: renovate-bot

package.json

@@ -39,7 +39,7 @@
     "gatsby-mdx": "0.1.4",
     "gatsby-plugin-google-analytics": "2.0.12",
     "gatsby-plugin-manifest": "2.0.15",
-    "gatsby-plugin-offline": "2.0.22",
+    "gatsby-plugin-offline": "3.0.26",
     "gatsby-plugin-react-helmet": "3.0.5",
     "gatsby-plugin-sass": "2.0.8",
     "gatsby-plugin-zopfli": "1.0.4",