Update changelog for v0.6.2 release

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## v0.6.2
+- Fixed bug deleting the last character in the buffer in vi mode (#450)
+- Degrade gracefully when user doesn't have `zsh/system` module installed (#447)
+
 ## v0.6.1
 - Fixed bug occurring when `_complete` had been aliased (#443)