Update CHANGELOG

Author: andreynering

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Fixed panic bug when assigning a global variable
   ([#229](https://github.com/go-task/task/issues/229), [#243](https://github.com/go-task/task/issues/234)).
+- A task with `method: checksum` will now re-run if generated files are deleted
+  ([#228](https://github.com/go-task/task/pull/228), [#238](https://github.com/go-task/task/issues/238)).
 
 ## v2.6.0 - 2019-07-21