Update theme to v2

Author: trevorblades

docs/gatsby-config.js

@@ -1,9 +1,12 @@
+const themeOptions = require('gatsby-theme-apollo-docs/theme-options');
+
 module.exports = {
   pathPrefix: '/docs/apollo-server',
-  __experimentalThemes: [
+  plugins: [
     {
       resolve: 'gatsby-theme-apollo-docs',
       options: {
+        ...themeOptions,
         root: __dirname,
         subtitle: 'Apollo Server',
         description: 'A guide to using Apollo Server',

docs/package-lock.json

@@ -6,6 +6,8 @@
   },
   "dependencies": {
     "gatsby": "2.13.83",
-    "gatsby-theme-apollo-docs": "1.4.1"
+    "gatsby-theme-apollo-docs": "^2.0.0",
+    "react": "^16.9.0",
+    "react-dom": "^16.9.0"
   }
 }