QUICKSTART: config.json bugfix

docs/QUICKSTART.md

@@ -276,7 +276,7 @@ We can add these endpoints to our `config.json`:
             "https://somevps1.hostingprovider.example/",
             "https://d11ipsexample.cloudfront.net"
         ],
-        concurrency: 2
+        "concurrency": 2
     }],
     "loggedComponents": ["service-worker", "fetch", "cache"],
     "defaultPluginTimeout": 1000