chore(*): Updating the changelog with the sorting strategy changes

CHANGELOG.md

@@ -173,13 +173,16 @@ When you focus a specific cell and press one of the following key combinations,
     - **Breaking change** cell selection is preserved when the focus is moved to group row.
     - Introduced `onFocusChange` event. The event is cancelable and output argument from type `IFocusChangeEventArgs`;
     - For more detailed information see the [official keyboard navigation specification](https://github.com/IgniteUI/igniteui-angular/wiki/igxGrid-Specification#kb-navigation).
-    
-## 6.1.8
+
+## 6.1.9
 
 ### General
 
-- `sortStrategy` input exposed to provide custom sort strategy for the `IgxColumnComponent`. The custom strategy should implement the `ISortingStrategy` interface, or can extend the base `SortingStrategy` class and override all or some of its public/protected members.
+- `sortStrategy` input exposed to provide custom sort strategy for the `IgxColumnComponent`. The custom strategy should implement the `ISortingStrategy` interface, or can extend the base `DefaultSortingStrategy` class and override all or some of its public/protected members.
+- The previously optional `ignoreCase` and `strategy` of the `ISortingExpression` interface are no longer optional. In order to use our default sorting strategy in expressions built programmatically, you need to pass `DefaultSortingStrategy.instance()` or any implementation of the `ISortingStrategy` interface.  
 - `groupingComparer` input exposed to provide custom grouping compare function for the `IgxColumnComponent`. The function receives two values and should return `0` if they are to considered members of the same group.
+
+## 6.1.8
 
 ### Bug fixes