chore(changelog): remove 8.2.x tag and move the changes under 8.2.0

Closes #5323

Author: Aleksandyr

CHANGELOG.md

@@ -2,12 +2,10 @@
 
 All notable changes for each version of this project will be documented in this file.
 
-## 8.2.x
+## 8.2.0
 - `IgxGrid`, `IgxTreeGrid`, `IgxHierarchicalGrid`
     - `[filterStrategy] - input that allows you to override the default filtering strategy`
 
-## 8.2.0
-
 ### New theme
 Ignite UI for angular now have a new theme that mimics Microsoft "Fluent" design system.  
 Depending on your use case you can use one of the following mixins: