fix: examples/with-next-offline/package.json to reduce vulnerabilities (

#20)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-SSRI-1246392

examples/with-next-offline/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "next": "canary",
-    "next-offline": "4.0.6",
+    "next-offline": "5.0.0",
     "react": "16.12.0",
     "react-dom": "16.12.0"
   },