Update site-design-pnp-provisioning.md (SharePoint#1667)

URL to appregnew.aspx was incorrect.

Author: rdtechie

docs/declarative-customization/site-design-pnp-provisioning.md

@@ -27,7 +27,7 @@ You'll use these components to trigger the PnP provisioning code after you creat
 
 To set up app-only access, you need to have two different pages on your tenant - one on the regular site, and the other on your SharePoint administration site.
 
-1. Go to following URL in your tenant: `https://[yourtenant].sharepoint.com/_layouts/appregnew.aspx` (you can go to any site, but for now pick the root site).
+1. Go to following URL in your tenant: `https://[yourtenant].sharepoint.com/_layouts/15/appregnew.aspx` (you can go to any site, but for now pick the root site).
 1. Choose the **Generate** button next to the **Client Id** and **Client Secret** fields.
 1. Enter a title for your app, such as "Site Provisioning".
 1. In the **App Domain** box, enter **localhost**.