Filter all hidden directories when adding to load-path

prelude-add-subfolders-to-load-path currently recurses into ".git"
directories for example.  Seems reasonable to skip any "hidden"
directory prefixed with a "."

init.el

@@ -73,8 +73,7 @@ by Prelude.")
  (dolist (f (directory-files parent-dir))
    (let ((name (expand-file-name f parent-dir)))
      (when (and (file-directory-p name)
-                (not (equal f ".."))
-                (not (equal f ".")))
+                (not (string-prefix-p "." f)))
        (add-to-list 'load-path name)
        (prelude-add-subfolders-to-load-path name)))))