fixed comments

src/main/java/mate/academy/service/AuthenticationService.java

@@ -12,13 +12,10 @@ public class AuthenticationService {
      * @return true if user by email exists and passed password is equal to user's password.
      * Return false in any other cases.
      */
-    private UserService userService = new UserService();
+    private final UserService userService = new UserService();
 
     public boolean login(String email, String password) {
         User user = userService.findByEmail(email);
-        if (user != null) {
-            return user.getPassword().equals(password);
-        }
-        return false;
+        return user != null && user.getPassword().equals(password);
     }
 }