Replace set_var usage in examples (#829)

* examples: Fix inconsistent toml formatting

* examples: Replace set_var usage

examples/versioning/Cargo.toml

@@ -8,4 +8,4 @@ publish = false
 axum = { path = "../../axum" }
 tokio = { version = "1.0", features = ["full"] }
 tracing = "0.1"
-tracing-subscriber = { version="0.3", features = ["env-filter"] }
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }

examples/versioning/src/main.rs

@@ -13,14 +13,16 @@ use axum::{
     Router,
 };
 use std::{collections::HashMap, net::SocketAddr};
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 #[tokio::main]
 async fn main() {
-    // Set the RUST_LOG, if it hasn't been explicitly defined
-    if std::env::var_os("RUST_LOG").is_none() {
-        std::env::set_var("RUST_LOG", "example_versioning=debug")
-    }
-    tracing_subscriber::fmt::init();
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::new(
+            std::env::var("RUST_LOG").unwrap_or_else(|_| "example_versioning=debug".into()),
+        ))
+        .with(tracing_subscriber::fmt::layer())
+        .init();
 
     // build our application with some routes
     let app = Router::new().route("/:version/foo", get(handler));