style: fix tslint warning

For AngularCli tslint.json sais that quote marks has to be single.

Closes angular#563

Author: zalog

docs/1-install-and-setup.md

@@ -67,10 +67,10 @@ import { AngularFireModule } from 'angularfire2';
 
 // Must export the config
 export const firebaseConfig = {
-  apiKey: "<your-key>",
-  authDomain: "<your-project-authdomain>",
-  databaseURL: "<your-database-URL>",
-  storageBucket: "<your-storage-bucket>"
+  apiKey: '<your-key>',
+  authDomain: '<your-project-authdomain>',
+  databaseURL: '<your-database-URL>',
+  storageBucket: '<your-storage-bucket>'
 };
 
 @NgModule({