- add dependency to xml library

- update to 0.38.2:
* Fix another regression caused by new feature to merge sibling groups
* Fix regression caused by new feature to merge sibling groups
* Fix issue with dropping xlink:href attribute when collapsing referenced gradients
* Fix issue with dropping ID while de-duplicating gradients
* Improve `--shorten-ids` so it re-maps IDs that are already used in the
document if they're shorter
* Fix whitespace handling for SVG 1.2 flowed text
* Improvement: Merge sibling `` nodes with identical attributes
* Improve performance of XML serialization
* Improve performance of gradient de-duplication
* Some general performance improvements