Use a polyfill for fetch

package.json

@@ -19,7 +19,8 @@
     "@kadira/storybook-database": "^2.0.1",
     "body-parser": "^1.15.2",
     "lodash": "^4.15.0",
-    "lowdb": "^0.13.1"
+    "lowdb": "^0.13.1",
+    "whatwg-fetch": "^1.0.0"
   },
   "peerDependencies": {
     "express": "^4.0.0"

src/client/bundledPersister.js

@@ -1,3 +1,4 @@
+import 'whatwg-fetch';
 import lowdb from 'lowdb';
 import lodash from 'lodash';
 import Database from '../shared/database';

src/client/devServerPersister.js

@@ -1,3 +1,5 @@
+import 'whatwg-fetch';
+
 export default class DevServerPersister {
   constructor({ url }) {
     this.url = url;