examples/Cargo.toml: tracing-subscriber update

It was required due to the book using `extern crate` syntax. Divergence
of version used across the project caused ambiguity and errors on book
tests build.

Author: wprzytula

examples/Cargo.toml

@@ -13,7 +13,7 @@ rustyline-derive = "0.6"
 scylla = {path = "../scylla", features = ["ssl"]}
 tokio = {version = "1.1.0", features = ["full"]}
 tracing = "0.1.25"
-tracing-subscriber = "0.2.16"
+tracing-subscriber = "0.3.14"
 chrono = "0.4"
 uuid = "1.0"
 tower = "0.4"