修复错误的默认 ACL 规则，之前是：
```
{allow, {username, "^dashboard?"}, subscribe, ["$SYS/#"]}.
```
但执行正则表达式的匹配应该使用 `{re, "^dashboard$"}`：
```
{allow, {username, {re, "^dashboard$"}}, subscribe, ["$SYS/#"]}.
```