doc(tokio): Set keep_alive to false on hyper clients.

This prevents hanging event loops.

examples/test-svc-acct/src/main.rs

@@ -13,7 +13,9 @@ fn main() {
     let creds =
         yup_oauth2::service_account_key_from_file(path::Path::new("serviceaccount.json")).unwrap();
     let https = HttpsConnector::new(1).expect("tls");
-    let client = Client::builder().build::<_, hyper::Body>(https);
+    let client = Client::builder()
+        .keep_alive(false)
+        .build::<_, hyper::Body>(https);
 
     let mut sa = yup_oauth2::ServiceAccountAccess::new(creds, client);
 
@@ -29,7 +31,6 @@ fn main() {
             println!("cached token is {:?} and should be identical", tok);
             Ok(())
         });
-    let all = fut.join(fut2);
-    let mut rt = tokio::runtime::Runtime::new().unwrap();
-    rt.block_on(all).unwrap();
+    let all = fut.join(fut2).then(|_| Ok(()));
+    tokio::run(all)
 }