SPFx dev setup doc update

Author: VesaJuvonen

docs/spfx/set-up-your-developer-tenant.md

@@ -1,7 +1,7 @@
 ---
 title: Set up your Office 365 tenant
 description: Build and deploy client-side web parts using the SharePoint Framework by setting up an Office 365 tenant.
-ms.date: 03/14/2018
+ms.date: 08/20/2018
 ms.prod: sharepoint
 ---