update changelog for release (#2383)

charlotteliang · web-flow · commit 571c82547e35 · 2019-02-12T14:02:14.000-08:00
diff --git a/Firebase/Messaging/CHANGELOG.md b/Firebase/Messaging/CHANGELOG.md
@@ -1,3 +1,6 @@
+# 2019-02-20 -- v3.3.1
+- Internal code cleanup.
+
 # 2019-01-22 -- v3.3.0
 - Use the new registerInternalLibrary API to register with FirebaseCore. (#2137)
 
