Update routing.md (#2786)

Added "is" for clarity in the opening sentence.

src/guide/scaling-up/routing.md

@@ -2,7 +2,7 @@
 
 ## Client-Side vs. Server-Side Routing {#client-side-vs-server-side-routing}
 
-Routing on the server side means the server sending a response based on the URL path that the user is visiting. When we click on a link in a traditional server-rendered web app, the browser receives an HTML response from the server and reloads the entire page with the new HTML.
+Routing on the server side means the server is sending a response based on the URL path that the user is visiting. When we click on a link in a traditional server-rendered web app, the browser receives an HTML response from the server and reloads the entire page with the new HTML.
 
 In a [Single-Page Application](https://developer.mozilla.org/en-US/docs/Glossary/SPA) (SPA), however, the client-side JavaScript can intercept the navigation, dynamically fetch new data, and update the current page without full page reloads. This typically results in a more snappy user experience, especially for use cases that are more like actual "applications", where the user is expected to perform many interactions over a long period of time.