Simplify async scheduler

Sources/Run/main.swift

@@ -4,6 +4,9 @@ import Vapor
 var env = Environment.production
 try LoggingSystem.bootstrap(from: &env)
 let app = Application(env)
-defer { app.shutdown() }
+defer {
+    shutdown()
+    app.shutdown()
+}
 try configure(app)
 try app.run()