update (fix) some site.manifest values

as suggested by Chrome browser Developer Tools

static/site.webmanifest

@@ -3,6 +3,7 @@
   "name": "OE7DRT",
   "short_name": "OE7DRT",
   "description": "Personal website of Dominic Reich “OE7DRT” – austrian amateur radio station – licensed since November 2019.",
+  "id": "/?utm_source=homescreen",
   "start_url": "/?utm_source=homescreen",
   "theme_color": "rgb(25,55,71)",
   "background_color": "#fff",
@@ -13,50 +14,42 @@
     {
       "src": "/icons/icon-72x72.png",
       "sizes": "72x72",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-96x96.png",
       "sizes": "96x96",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-128x128.png",
       "sizes": "128x128",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-144x144.png",
       "sizes": "144x144",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-152x152.png",
       "sizes": "152x152",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-192x192.png",
       "sizes": "192x192",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-384x384.png",
       "sizes": "384x384",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     },
     {
       "src": "/icons/icon-512x512.png",
       "sizes": "512x512",
-      "type": "image/png",
-      "purpose": "any maskable" 
+      "type": "image/png"
     }
   ]
 }