Update changelog

Author: aeisenberg

extensions/ql-vscode/CHANGELOG.md

@@ -7,6 +7,7 @@
 - Respect VSCode's i18n locale setting when formatting dates and sorting strings.
 - Allow the opening of large Sarif files externally from VSCode.
 - Add new 'CodeQL: Compare Query' command that shows the differences between two queries.
+- Allow multiple items in the query history view to be removed in one operation.
 
 ## 1.2.2 - 8 June 2020