Fix amp-web-push helper iframe configuration URL
Fix amp-web-push helper iframe configuration URL

Change the <amp-web-push> configuration property "helper-frame-url"
value from "amphtml-helper-frame.html" to "amp-helper-frame.html".
"amp-helper-frame.html" is the file supplied by OneSignal's WordPress
plugin, and using "amphtml-helper-frame.html" causes a 404 Not Found
error.

ahmedkaludi/Accelerated-Mobile-Pages,ahmedkaludi/Accelerated-Mobile-Pages