extract_zstd: fix typo

Author: scivision

+stdlib/extract_zstd.m

@@ -31,7 +31,7 @@ function extract_zstd_bin(archive, out_dir)
   out_dir (1,1) string
 end
 
-exe = which("zstd");
+exe = stdlib.which("zstd");
 assert(~isempty(exe), "need to have Zstd installed: https://github.com/facebook/zstd")
 
 tar_arc = tempname;