Update CHANGELOG.md to add bold to Breaking change

Author: Ellet

CHANGELOG.md

@@ -3,7 +3,7 @@
 All notable changes to this project will be documented in this file.
 
 ## 9.3.0
-* Breaking change: `Document.fromHtml(html)` is now returns `Document` instead of `Delta`, use `DeltaX.fromHtml` to return `Delta`
+* **Breaking change**: `Document.fromHtml(html)` is now returns `Document` instead of `Delta`, use `DeltaX.fromHtml` to return `Delta`
 * Update old deprecated api from Flutter 3.19
 
 ## 9.2.14