Remove trailing whitespace from the CHANGELOG

Author: davep

CHANGELOG.md

@@ -14,7 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed issue where narrow TextArea would repeatedly wrap due to scrollbar appearing/disappearing https://github.com/Textualize/textual/pull/4334
 - Fix progress bar ETA not updating when setting `total` reactive https://github.com/Textualize/textual/pull/4316
 
-### Changed 
+### Changed
 
 - ProgressBar won't show ETA until there is at least one second of samples https://github.com/Textualize/textual/pull/4316