Replace set_var usage in examples (#829)

* examples: Fix inconsistent toml formatting

* examples: Replace set_var usage

examples/tokio-postgres/Cargo.toml

@@ -8,7 +8,7 @@ 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"] }
 bb8 = "0.7.1"
 bb8-postgres = "0.7.0"
 tokio-postgres = "0.7.2"

examples/tokio-postgres/src/main.rs

@@ -15,14 +15,16 @@ use bb8::{Pool, PooledConnection};
 use bb8_postgres::PostgresConnectionManager;
 use std::net::SocketAddr;
 use tokio_postgres::NoTls;
+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_tokio_postgres=debug")
-    }
-    tracing_subscriber::fmt::init();
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::new(
+            std::env::var("RUST_LOG").unwrap_or_else(|_| "example_tokio_postgres=debug".into()),
+        ))
+        .with(tracing_subscriber::fmt::layer())
+        .init();
 
     // setup connection pool
     let manager =