title: PWA icons are not used in iOS 11.3
body: <p>Now I'm testing PWA on iOS 11.3 and I use the manifest.json file below:</p>
  
  <pre><code>{
    "name": "Maplat PWA Sample",
    "short_name": "Maplat PWA",
    "background_color": "#fc980c",
    "icons": [{
      "src": "/Maplat/pwa/icon-96.png",
      "sizes": "96x96",
      "type": "image/png"
    },{
      "src": "/Maplat/pwa/icon-144.png",
      "sizes": "144x144",
      "type": "image/png"
    },{
      "src": "/Maplat/pwa/icon-192.png",
      "sizes": "192x192",
      "type": "image/png"
    },{
      "src": "/Maplat/pwa/icon-256.png",
      "sizes": "256x256",
      "type": "image/png"
    }],
    "start_url": "/Maplat/debug.html?overlay=true",
    "display": "standalone"
  }
  </code></pre>
  
  <p>This works well except icon setting.
  In my iOS 11.3 on iPhoneX, icon files are not shown on home screen but screen capture is used as launcher button.</p>
  
  <p>I compared my manifest with other sites, like <a href="https://www.ft.com/" rel="noreferrer">https://www.ft.com/</a> or <a href="https://r.nikkei.com/" rel="noreferrer">https://r.nikkei.com/</a>, but I couldn't find any differences in icon settings.
  Icons of these sites work well with PWA on iOS 11.3.</p>
  
  <p>What is wrong in my manifest.json?</p>
  
  <p>P.S. My manifest.json works well with Android Chrome.</p>