etc/ORG-NEWS: Rename `org-persist-path' to `org-persist-directory'

* etc/ORG-NEWS (New library =org-persist.el= implements variable
persistence across Emacs sessions): Fix leftover variable name after
3b4822499.

etc/ORG-NEWS

@@ -44,7 +44,7 @@ The cache persistence can be controlled via
 
 *** New library =org-persist.el= implements variable persistence across Emacs sessions
 
-The library stored variable data in ~org-persist-path~ (set to XDG
+The library stored variable data in ~org-persist-directory~ (set to XDG
 cache dir by default).
 
 The entry points are ~org-persist-register~, ~org-persist-unregister~,