restful_example: upgrade axios

examples/protocols/http_server/restful_server/front/web-demo/package.json

@@ -8,7 +8,7 @@
     "lint": "vue-cli-service lint"
   },
   "dependencies": {
-    "axios": "^0.18.0",
+    "axios": "^0.21.1",
     "core-js": "^2.6.5",
     "vue": "^2.6.10",
     "vue-router": "^3.0.3",