Update index.md (#3129)

Add missing word

Author: mrlife

entity-framework/core/change-tracking/index.md

@@ -16,7 +16,7 @@ This document presents an overview of Entity Framework Core (EF Core) change tra
 > You can run and debug into all the code in this document by [downloading the sample code from GitHub](https://github.com/dotnet/EntityFramework.Docs/tree/master/samples/core/ChangeTracking/ChangeTrackingInEFCore).
 
 > [!TIP]
-> For simplicity, this document uses and references synchronous methods such as <xref:Microsoft.EntityFrameworkCore.DbContext.SaveChanges%2A> rather their async equivalents such as <xref:Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync%2A>. Calling and awaiting the async method can be substituted unless otherwise noted.
+> For simplicity, this document uses and references synchronous methods such as <xref:Microsoft.EntityFrameworkCore.DbContext.SaveChanges%2A> rather than their async equivalents such as <xref:Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync%2A>. Calling and awaiting the async method can be substituted unless otherwise noted.
 
 ## How to track entities