set default root url

app.json

@@ -13,6 +13,10 @@
             "value": "",
             "required": true
         },
+        "TALK_ROOT_URL": {
+          "value": "http://0.0.0.0",
+          "required": true
+        },
         "NODE_ENV": "production",
         "REWRITE_ENV": "TALK_MONGO_URL:MONGO_URI,TALK_REDIS_URL:REDIS_URL,TALK_SMTP_HOST:MAILGUN_SMTP_SERVER,TALK_SMTP_PORT:MAILGUN_SMTP_PORT,TALK_SMTP_USERNAME:MAILGUN_SMTP_LOGIN,TALK_SMTP_PASSWORD:MAILGUN_SMTP_PASSWORD",
         "NPM_CONFIG_PRODUCTION": "false"