message: [gatsby-plugin-vercel-builder] Strip `assetPrefix` from `pathPrefix`
  Removes the `assetPrefix` value from the `pathPrefix` config value,
  since Gatsby concats them for some reason.
diff: @@ -8,4 +8,5 @@ module.exports = {
  },
  plugins: [],
  pathPrefix: '/foo',
  + assetPrefix: 'https://example.com',
  };
  