move userService to class level

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

@@ -3,6 +3,7 @@
 import mate.academy.model.User;
 
 public class AuthenticationService {
+    UserService userService = new UserService();
     /**
      * Imagine that some user wants to log in to your site.
      * You should check if user credentials (login and password) are valid or not.
@@ -13,7 +14,6 @@ public class AuthenticationService {
      * Return false in any other cases.
      */
     public boolean login(String email, String password) {
-        UserService userService = new UserService();
         User user = userService.findByEmail(email);
         return user != null && user.getPassword().equals(password);
     }