fix(auth): improve typings for onAuthStateChanged

Author: jsayol

typings/app.d.ts

@@ -123,7 +123,7 @@ declare namespace firebase.auth {
     currentUser : firebase.User | null ;
     fetchProvidersForEmail (email : string ) : firebase.Promise < any > ;
     getRedirectResult ( ) : firebase.Promise < any > ;
-    onAuthStateChanged (nextOrObserver : Object , error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
+    onAuthStateChanged (nextOrObserver : Object | ((user: firebase.User | null) => any), error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
     onIdTokenChanged (nextOrObserver : Object , error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
     sendPasswordResetEmail (email : string ) : firebase.Promise < any > ;
     signInAndRetrieveDataWithCredential (credential : firebase.auth.AuthCredential ) : firebase.Promise < any > ;

typings/firebase.d.ts

@@ -123,7 +123,7 @@ declare namespace firebase.auth {
     currentUser : firebase.User | null ;
     fetchProvidersForEmail (email : string ) : firebase.Promise < any > ;
     getRedirectResult ( ) : firebase.Promise < any > ;
-    onAuthStateChanged (nextOrObserver : Object , error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
+    onAuthStateChanged (nextOrObserver : Object | ((user: firebase.User | null) => any), error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
     onIdTokenChanged (nextOrObserver : Object , error ? : (a : firebase.auth.Error ) => any , completed ? : ( ) => any ) : ( ) => any ;
     sendPasswordResetEmail (email : string ) : firebase.Promise < any > ;
     signInAndRetrieveDataWithCredential (credential : firebase.auth.AuthCredential ) : firebase.Promise < any > ;