Mention hosting bundle installation requirement for 2.1 migration (dotnet#8075)

Fixes dotnet#7919

[Internal Review Page](https://review.docs.microsoft.com/en-us/aspnet/core/migration/20_21?branch=pr-en-us-8075&view=aspnetcore-2.1#additional-changes)

Author: scottaddie

aspnetcore/migration/20_21.md

@@ -3,7 +3,7 @@ title: Migrate from ASP.NET Core 2.0 to 2.1
 author: rick-anderson
 description: This article covers the basics of migrating an ASP.NET Core 2.0 app to 2.1.
 ms.author: riande
-ms.date: 07/25/2018
+ms.date: 08/14/2018
 uid: migration/20_21
 ---
 # Migrate from ASP.NET Core 2.0 to 2.1
@@ -125,7 +125,7 @@ The default 2.1 Identity UI doesn't currently provide significant new features o
 
 If you've made non-trivial changes to the template generated Identity code:
 
-* The preceding advantages probably do **not** justify converting to the the RCL version.
+* The preceding advantages probably do **not** justify converting to the RCL version.
 * You can keep your ASP.NET Core 2.0 Identity code, it's fully supported.
 
 Identity 2.1 exposes endpoints with the `Identity` area. For example, the follow table shows examples of Identity endpoints that change from 2.0 to 2.1:
@@ -226,5 +226,6 @@ See [GDPR support in ASP.NET Core](xref:security/gdpr) for information on the pr
 
 ## Additional changes
 
+* If hosting the app on Windows with IIS, install the latest [.NET Core Hosting Bundle](xref:host-and-deploy/iis/index#install-the-net-core-hosting-bundle).
 * [SetCompatibilityVersion](xref:fundamentals/startup#setcompatibilityversion)
 * [Transport configuration](xref:fundamentals/servers/kestrel#transport-configuration)