bumped libxml version

this is zach's work from the libxml bump. a few things to note.

* these changes were sitting in the cyclusci user space uncommitted
* the ciclus repo in the cyclusci user space is configured with @zwelchWI's credentials
* we should agree on a workflow to update the ciclus repo in the cyclusci user space
  * my workflow is local commit, push to ciclus, pull in changes on the submit node