This fixes the following `cargo audit` warning:

```
Crate:         tokio
Version:       1.13.0
Title:         Data race when sending and receiving after closing a `oneshot` channel
Date:          2021-11-16
ID:            RUSTSEC-2021-0124
URL:           https://rustsec.org/advisories/RUSTSEC-2021-0124
Solution:      Upgrade to >=1.8.4, <1.9.0 OR >=1.13.1
```

Versions changed:

```
Updating tokio v1.13.0 -> v1.14.0
Updating tokio-macros v1.5.1 -> v1.6.0
```

These can't be fixed for now, and are causing us to miss more important audit vulnerabilities.