Update making-a-progressive-web-app.md (#5658)

Author: jakeboone02

docusaurus/docs/making-a-progressive-web-app.md

@@ -61,7 +61,7 @@ following into account:
    app works offline!" message) and also let them know when the service worker has
    fetched the latest updates that will be available the next time they load the
    page (showing a "New content is available once existing tabs are closed." message). Showing
-   this messages is currently left as an exercise to the developer, but as a
+   these messages is currently left as an exercise to the developer, but as a
    starting point, you can make use of the logic included in [`src/serviceWorker.js`](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/src/serviceWorker.js), which
    demonstrates which service worker lifecycle events to listen for to detect each
    scenario, and which as a default, just logs appropriate messages to the