Update dependency xmldom

[karfau]

Switching from package xmldom to @xmldom/xmldom, which resolves the security issue present in latest xmldom version 0.6.0: https://github.com/xmldom/xmldom/security/advisories/GHSA-5fg8-2547-mr8q

The reason is that the maintainers were forced to switch to a scoped package since 0.7.0: https://github.com/xmldom/xmldom/issues/271

• I used node 12 to run npm install.
• I executed npm run test on my machine without failure
• I tried to run npm run prepublishOnly but it failed in make test with one test timing out. After running make force-install-libs it fails in the step make dist (Makefile line 39), but from the error message it doesn't look like it's an issue related to this PR
• This makes #35 obsolete

I'm one of the xmldom maintainers. Don't hesitate to ask me questions.

https://github.com/xmldom/xmldom/blob/master/CHANGELOG.md