Update stdlib module to latest 4.x

The latest verion 4.1.0 stdlib module has some new functions added
that are useful. Specficially, the delete_undef_values function had
been added to ther 4.x branch. This should be compatible with the
existing stdlib module we are using, which is also version 4.1.0.
Merge pull request #34 from rohara/update_stdlib

Update stdlib module to latest 4.x