Downgrade Jackson dependency

Jackson was upgraded to 2.3.0 which contains a bug that breaks RESTEasy. RESTEasy currently uses 2.2.1. Downgrading to at least 2.2.3, which is what CR1 is at, seems to resolve this issue.

We should likely keep the version aligned with RESTEasy, but since CR1 was using 2.2.3 with no issues, I think reverting back to that should be fine.