message: Add default networkFirst offline handling
diff: {
  "name": "Swap.Online",
  + "short_name": "Swap.Online",
  "version": "1.3.1",
  "manifest_version": 2,
  "description": "Swap.Online Chrome Extension",
  "homepage_url": "https://swap.online/",
  - "icons": {
  - "16": "extension/images/icons/icon-16.png",
  - "32": "extension/images/icons/icon-32.png",
  - "192": "extension/images/icons/icon-196.png"
  + "theme_color": "#fff",
  + "background_color": "#fff",
  + "icons": [
  + {
  + "src": "extension/images/icons/icon-16.png",
  + "type": "image/png",
  + "sizes": "16x16"
  + },
  + {
  + "src": "extension/images/icons/icon-32.png",
  + "type": "image/png",
  + "sizes": "32x32"
  },
  + {
  + "src": "extension/images/icons/icon-196.png",
  + "type": "image/png",
  + "sizes": "192x192"
  + }
  + ],
  "options_page": "application/index.html",
  "browser_action": {
  "default_icon": "extension/images/icons/icon-32.png",
  "scripts": ["./extension/js/background.js"],
  "persistent": false
  },
  - "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'"
  + "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
  + "start_url": "/"
  }
  