Problems updating the Raindrops theme

As soon as the theme of the raindrops theme is updated, Custom Menu Wizard Widget presents the code on the cover page:

Warning: Declaration of Custom_Menu_Wizard_Walker :: walk ($ elements, $ max_depth) should be compatible with Walker :: walk ($ elements, $ max_depth, … $ args) in /web/htdocs/www.studisemeriani.it/home/ portal / wp-content / plugins / custom-menu-wizard / include / class.walker.php online 1320

Warning: Declaration of Custom_Menu_Wizard_Sorter :: walk ($ elements, $ max_depth = 0) should be compatible with Walker :: walk ($ elements, $ max_depth, … $ args) in /web/htdocs/www.studisemeriani.it/ home / portal / wp-content / plugins / custom-menu-wizard / include / class.sorter.php on line 73

How can I solve it?

The page I need help with: [log in to see the link]