tweak(default): add binding for undo-tree

This also makes the check for the presence of vundo consistent with the
rest of the file by using modulep! instead of fboundp.

modules/config/default/+evil-bindings.el

@@ -760,8 +760,9 @@
              ((modulep! :completion helm)      #'swiper-isearch-thing-at-point))
        :desc "Dictionary"                   "t" #'+lookup/dictionary-definition
        :desc "Thesaurus"                    "T" #'+lookup/synonyms
-       (:when (fboundp 'vundo)
-         :desc "Undo history"               "u" #'vundo))
+       :desc "Undo history"                 "u"
+       (cond ((modulep! :emacs undo +tree)     #'undo-tree-visualize)
+             ((modulep! :emacs undo)           #'vundo)))
 
       ;;; <leader> t --- toggle
       (:prefix-map ("t" . "toggle")