Update links to 5x api docs on use middleware page (#2039)

Co-authored-by: bjohansebas <103585995+bjohansebas@users.noreply.github.com>

en/guide/using-middleware.md

@@ -10,7 +10,7 @@ redirect_from: "/guide/using-middleware.html"
 
 Express is a routing and middleware web framework that has minimal functionality of its own: An Express application is essentially a series of middleware function calls.
 
-_Middleware_ functions are functions that have access to the [request object](/{{ page.lang }}/4x/api.html#req)  (`req`), the [response object](/{{ page.lang }}/4x/api.html#res) (`res`), and the next middleware function in the application's request-response cycle. The next middleware function is commonly denoted by a variable named `next`.
+_Middleware_ functions are functions that have access to the [request object](/{{ page.lang }}/5x/api.html#req)  (`req`), the [response object](/{{ page.lang }}/5x/api.html#res) (`res`), and the next middleware function in the application's request-response cycle. The next middleware function is commonly denoted by a variable named `next`.
 
 Middleware functions can perform the following tasks:
 
@@ -34,7 +34,7 @@ You can also load a series of middleware functions together, which creates a sub
 
 <h2 id='middleware.application'>Application-level middleware</h2>
 
-Bind application-level middleware to an instance of the [app object](/{{ page.lang }}/4x/api.html#app) by using the `app.use()` and `app.METHOD()` functions, where `METHOD` is the HTTP method of the request that the middleware function handles (such as GET, PUT, or POST) in lowercase.
+Bind application-level middleware to an instance of the [app object](/{{ page.lang }}/5x/api.html#app) by using the `app.use()` and `app.METHOD()` functions, where `METHOD` is the HTTP method of the request that the middleware function handles (such as GET, PUT, or POST) in lowercase.
 
 This example shows a middleware function with no mount path. The function is executed every time the app receives a request.
 
@@ -249,9 +249,9 @@ functions that were previously included with Express are now in separate modules
 
 Express has the following built-in middleware functions:
 
-- [express.static](/en/4x/api.html#express.static) serves static assets such as HTML files, images, and so on.
-- [express.json](/en/4x/api.html#express.json) parses incoming requests with JSON payloads. **NOTE: Available with Express 4.16.0+**
-- [express.urlencoded](/en/4x/api.html#express.urlencoded) parses incoming requests with URL-encoded payloads.  **NOTE: Available with Express 4.16.0+**
+- [express.static](/en/5x/api.html#express.static) serves static assets such as HTML files, images, and so on.
+- [express.json](/en/5x/api.html#express.json) parses incoming requests with JSON payloads. **NOTE: Available with Express 4.16.0+**
+- [express.urlencoded](/en/5x/api.html#express.urlencoded) parses incoming requests with URL-encoded payloads.  **NOTE: Available with Express 4.16.0+**
 
 <h2 id='middleware.third-party'>Third-party middleware</h2>