root_dir: no need for pattern

Author: scivision

+stdlib/root_dir.m

@@ -13,11 +13,9 @@
   p string
 end
 
-sep = characterListPattern("/" + filesep);
-
 r = repmat("", size(p));
 
-i = startsWith(p, sep);
+i = startsWith(p, ["/", filesep]);
 r(i) = extractBefore(p(i), 2);
 
 if ispc()