ts: update tokio fork for RUSTSEC-2021-0124

A data race condition was discovered in tokio, which can lead to memory corruption. This vulnerability affects our fork.

See:

• https://rustsec.org/advisories/RUSTSEC-2021-0124
• https://github.com/tokio-rs/tokio/issues/4225
• https://github.com/tokio-rs/tokio/pull/4226
• https://github.com/fengalin/tokio/pull/1

Fixes: #174 (closed)