add release notes for v3.2.4

I messed up the v3.2.3 release; forgot to backport the Dockerfile
changes, and also forgot to document the backported panic fix in the
expand package.

Let's pretend v3.2.3 didn't happen, since the tag was already pushed,
and do a v3.2.4. v3.2.3 isn't terribly broken either, so no need to
retract it.

CHANGELOG.md

@@ -1,9 +1,11 @@
 # Changelog
 
-## [3.2.3] - 2021-03-08
+## [3.2.4] - 2021-03-08
 
 - **cmd/shfmt**
   - Don't stop handling arguments when one results in a failure
+- **expand**
+  - Don't panic when a backslash is followed by EOF
 
 ## [3.2.2] - 2021-01-29
 
@@ -501,7 +503,7 @@ module in v3.
 
 Initial release.
 
-[3.2.3]: https://github.com/mvdan/sh/releases/tag/v3.2.3
+[3.2.4]: https://github.com/mvdan/sh/releases/tag/v3.2.4
 [3.2.2]: https://github.com/mvdan/sh/releases/tag/v3.2.2
 [3.2.1]: https://github.com/mvdan/sh/releases/tag/v3.2.1
 [3.2.0]: https://github.com/mvdan/sh/releases/tag/v3.2.0