Update to latest multi_xml to fix security vulnerability.

This is similar to the issue that affected Rails, which allowed various
nasty remote code exploits and/or SQL injection. Some details here:
https://gist.github.com/d7f6d9f4925f413621aa

Bumped version to 0.2.05
Merge pull request #27 from smulube/security_update

Update to latest multi_xml to fix security vulnerability.