[Helm] Fixing missing require for ‘db/helm-shortcuts’

Not quite sure whether it is necessary, but it seems to help.  A proper
understanding would be more reassuring, though.

site-lisp/db-utils.el

@@ -295,6 +295,7 @@ If FILE is not given, prompt for one."
 (defun db/helm-shortcuts ()
   "Open helm completion on common locations."
   (interactive)
+  (require 'helm-files)                 ; seems to be necessary
   (helm :sources '(db/helm-frequently-used-features
                    db/helm-frequently-visited-locations)))