Fix doc comment typo

Author: danroth27

src/Microsoft.AspNetCore.Http.Abstractions/Extensions/UseMiddlewareExtensions.cs

@@ -13,7 +13,7 @@
 namespace Microsoft.AspNetCore.Builder
 {
     /// <summary>
-    /// Extension methods for adding typed middlware.
+    /// Extension methods for adding typed middleware.
     /// </summary>
     public static class UseMiddlewareExtensions
     {
@@ -172,4 +172,4 @@ private static object GetService(IServiceProvider sp, Type type, Type middleware
             return service;
         }
     }
-}
+}