feature/evil: use magit-section-toggle if mode is derived from magit-mode

- Closes #359
- See also https://github.com/hlissner/doom-emacs/pull/359#issuecomment-359220633

modules/feature/evil/autoload/folds.el

@@ -88,7 +88,7 @@
   (interactive)
   (ignore-errors
     (call-interactively
-     (cond ((string-prefix-p "magit" (symbol-name major-mode))
+     (cond ((derived-mode-p 'magit-mode)
             #'magit-section-toggle)
            ((+evil-fold-p)
             #'+evil:fold-toggle)