Updated xmldom package to new namespace for vuln remediation

[chriswhite199]

Output from npm audit from current master shows critical severity for xmldom library:

xmldom  *
Severity: critical
xmldom allows multiple root nodes in a DOM - https://github.com/advisories/GHSA-crh6-fp67-6883
Misinterpretation of malicious XML input - https://github.com/advisories/GHSA-5fg8-2547-mr8q
No fix available
node_modules/xmldom

As per the package github page (https://github.com/xmldom/xmldom), they changed the namespace to @xmldom/xmldom so this PR updates that dependency in package.json and usage of the package in the source.

[mattnotmitt]

LGTM

[a3957273]

Notes: xmldom/xmldom#271

[a3957273]

Thanks for the improvement! :)