Update CHANGELOG.md

Author: James Foster

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 - Topmost installtion instructions now suggest `gem install arduino_ci` instead of using a `Gemfile`.  Reasons for using a `Gemfile` are listed and discussed separately further down the README.
+- Stream::readStreamUntil() no longer returns delimiter
 
 ### Removed
 - scanning of `library.properties`; this can and should now be performed by the standalone [`arduino-lint` tool](https://arduino.github.io/arduino-lint).