1527: updated CHANGELOG.md

Author: Vitaliy Boyko

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0).
 
 ## 5.1.1
 
+### Fixed
+
+- java.lang.NoClassDefFoundError: org/codehaus/plexus/util/StringUtils [#1235](https://github.com/magento/magento2-phpstorm-plugin/pull/1530)
+
 ## 5.1.0
 
 ### Fixed