Update tracing-subscriber requirement from 0.2 to 0.3

Updates the requirements on [tracing-subscriber](https://github.com/tokio-rs/tracing) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/tracing/releases)
- [Commits](tokio-rs/tracing@tracing-subscriber-0.2.0...tracing-subscriber-0.3.0)

---
updated-dependencies:
- dependency-name: tracing-subscriber
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -23,4 +23,4 @@ async-trait = "0.1"
 [dev-dependencies]
 tide = { version = "0.16", default-features = false, features = ["h1-server"] }
 async-std = { version = "1.9", features = ["attributes"] }
-tracing-subscriber = "0.2"
+tracing-subscriber = "0.3"