Bump tracing-subscriber from 0.2.25 to 0.3.0 (#40)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Xiangru Lian <[email protected]>

Author: dependabot[bot]

Cargo.lock

@@ -12,7 +12,7 @@ edition = "2018"
 [dependencies]
 tracing = "0.1"
 anyhow = "1"
-tracing-subscriber = "0.2"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 structopt = "0.3"
 cmd_lib = "1.3"
 ctrlc = "3.2"