Update changelog for release (firebase#857)

* Updates changelog in preparation for release

* Adds another change.

Author: protocol86

Firebase/Auth/CHANGELOG.md

@@ -1,3 +1,9 @@
+# v4.4.4
+- Addresses CLANG_WARN_OBJC_IMPLICIT_RETAIN_SELF warnings that surface in newer versions of
+  Xcode and CocoaPods.
+- Improves FIRUser documentation with clear message explaining when Firebase Auth attempts to validate
+  users and what happens when an invalidated user is detected (#694) .
+
 # v4.4.3
 - Adds an explicit dependency on CoreGraphics from Firebase Auth.