Update CHANGELOG for Firestore v0.9.4 (#556)

Author: wilhuff

Firestore/CHANGELOG.md

@@ -1,8 +1,9 @@
 # Unreleased
+
+# v0.9.4
 - [changed] Firestore no longer has a direct dependency on FirebaseAuth.
 - [fixed] Fixed a crash when using path names with international characters
   with persistence enabled.
-
 - [fixed] Addressed race condition during the teardown of idle streams (#490).
 
 # v0.9.3