RTDB 6.1.0 Changelog update (#3566)

Author: paulb777

Firebase/Database/CHANGELOG.md

@@ -1,9 +1,12 @@
 # Unreleased
+
+# v6.1.0
+- [fixed] Fix Catalyst Build issue. (#3512)
 - [feature] The SDK adds support for the Firebase Database Emulator. To connect
   to the emulator, specify "http://<emulator_host>/" as your Database URL
   (via `Database.database(url:)`).
   If you refer to your emulator host by IP rather than by domain name, you may
-  also need to specify a namespace ("http://<emulator_host>/?ns=<namespace>").
+  also need to specify a namespace ("http://<emulator_host>/?ns=<namespace>"). (#3491)
 
 # v6.0.0
 - [removed] Remove deprecated `childByAppendingPath` API. (#2763)