Update site.webmanifest

Author: philwareham

site.webmanifest

@@ -3,8 +3,8 @@
   "name": "Textpattern CMS Documentation",
   "start_url": "https://docs.textpattern.com",
   "icons": [
-    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
-    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png" }
+    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png", "purpose": "maskable any" },
+    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable any" }
   ],
   "background_color": "#ffffff",
   "theme_color": "#ffda44",