Update redis requirement from 0.20.1 to 0.21.0

Updates the requirements on [redis](https://github.com/mitsuhiko/redis-rs) to permit the latest version.
- [Release notes](https://github.com/mitsuhiko/redis-rs/releases)
- [Changelog](https://github.com/mitsuhiko/redis-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mitsuhiko/redis-rs/commits)

---
updated-dependencies:
- dependency-name: redis
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -12,7 +12,7 @@ keywords = ["sessions", "tide", "async-session", "redis"]
 categories = ["web-programming::http-server", "web-programming", "database"]
 
 [dependencies.redis]
-version = "0.20.1"
+version = "0.21.0"
 features = ["aio", "async-std-comp"]
 
 [dependencies]