Update fixtures with Prettier formatting

src/fixtures/gatsby/default.expected.js

@@ -1,8 +1,8 @@
 module.exports = {
-  pathPrefix: "/docs/",
+  pathPrefix: '/docs/',
   siteMetadata: {
     title: `My Gatsby Site`,
-    siteUrl: `https://www.yourdomain.tld`,
+    siteUrl: `https://www.yourdomain.tld`
   },
-  plugins: [],
-}
+  plugins: []
+}