Add a changelog entry for RTDB

Author: Feiyang1

packages/database/CHANGELOG.md

@@ -1,3 +1,4 @@
 # Unreleased
+- [fixed] Fixed an uglify issue in minified scripts (`firebase.js` and `firebase-database.js`) where multi-byte UTF-8 characters were encoded incorrectly. 
 - [changed] Improved consistency between the type annotations for `Query.on`/`Reference.on`, 
   `Query.off`/`Reference.off` and `Query.once`/`Reference.once` (#1188, #1204).