docs: update tracing-appender docs link to correct docs.rs URL (#3325)

The old documentation link for tracing-appender pointed to
https://tracing.rs/tracing-appender, which is no longer valid.
This commit updates the [docs-v0.2.x-url] in README.md to
use the correct and current documentation URL:
https://docs.rs/tracing-appender/

Author: VolodymyrBg

tracing-appender/README.md

@@ -20,7 +20,7 @@ Writers for logging events and spans
 [docs-badge]: https://docs.rs/tracing-appender/badge.svg
 [docs-url]: https://docs.rs/tracing-appender/0.2.2
 [docs-v0.2.x-badge]: https://img.shields.io/badge/docs-v0.2.x-blue
-[docs-v0.2.x-url]: https://tracing.rs/tracing-appender
+[docs-v0.2.x-url]: https://docs.rs/tracing-appender/
 [mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg
 [mit-url]: ../LICENSE
 [actions-badge]: https://github.com/tokio-rs/tracing/workflows/CI/badge.svg