fix typo in change note

Co-authored-by: Asger F <asgerf@github.com>

Author: erik-krogh

javascript/change-notes/2020-05-17-prototype-assignment.md

@@ -1,3 +1,3 @@
 lgtm,codescanning
 * The `js/prototype-polluting-assignment` query now flags assignments that may modify 
-  the build-in Object prototype where the property name originates from library input.
+  the built-in Object prototype where the property name originates from library input.