(Azure CXP) Fixed doc bug in step 4

Step 4 says to enter " Traffic Manager domain " name it should be "Custom domain" name.
https://github.com/MicrosoftDocs/azure-docs/issues/38630

Author: Grace-MacJones-MSFT

includes/custom-dns-web-site-enable-on-traffic-manager.md

@@ -24,7 +24,7 @@ If you have not already added your web app as a Traffic Manager endpoint, you mu
 
     ![](./media/custom-dns-web-site/dncmntask-cname-6.png)
 3. In the **Custom domains** blade, click **Add hostname**.
-4. Use the **Hostname** text boxes to enter the Traffic Manager domain name to associate with this web app.
+4. Use the **Hostname** text boxes to enter the custom domain name to associate with this web app.
 
     ![](./media/custom-dns-web-site/dncmntask-cname-8.png)
 5. Click **Validate** to save the domain name configuration.