Update api-client to modular Firebase

src/store/create-api-client.js

-import Firebase from 'firebase'
+import Firebase from 'firebase/app'
+import 'firebase/database'
 
-export default new Firebase('https://hacker-news.firebaseio.com/v0')
+const config = {
+  databaseURL: 'https://hacker-news.firebaseio.com'
+}
+const version = '/v0'
+
+Firebase.initializeApp(config)
+const api = Firebase.database().ref(version)
+export default api
\ No newline at end of file