fix: filter splash files in service worker

src/service-worker.js

@@ -26,6 +26,10 @@ const ON_DEMAND_CACHE = [
   {
     regex: /TwemojiCountryFlags\.woff2/,
     cache: ASSETS
+  },
+  {
+    regex: /_splash\.png$/,
+    cache: WEBPACK_ASSETS
   }
 ]
 
@@ -39,6 +43,7 @@ const assets = __assets__
   .filter(filename => !/emoji-.*?\.json$/.test(filename)) // useless to cache; it already goes in IndexedDB
   .filter(filename => !/screenshot-.*?\.png/.test(filename)) // only used during PWA installation, don't bother caching
   .filter(filename => !/TwemojiCountryFlags\.woff2/.test(filename)) // cache on-demand
+  .filter(filename => !/_splash\.png$/.test(filename)) // only used for iOS PWA splash screen, cache on-demand
 
 // `shell` is an array of all the files generated by webpack
 // also contains '/index.html' for some reason