Refactor for flask

Vapor3.1.10/Sources/App/app.swift

@@ -0,0 +1,12 @@
+import Vapor
+
+// Creates an instance of `Application`. This is called from `main.swift` in the run target.
+public func app(_ env: Environment) throws -> Application {
+    var config = Config.default()
+    var env = env
+    var services = Services.default()
+    try configure(&config, &env, &services)
+    let app = try Application(config: config, environment: env, services: services)
+    try boot(app)
+    return app
+}