Align with the version depended upon by the org.glassfish.jaxb and saaj-impl deps.

The cxf-parent pom specifies 2.0.0. We currently use 1.2.18.

Diff to 1.2.18: https://github.com/eclipse-ee4j/jaxb-fi/compare/1.2.18...2.1.0

Diff to 2.0.0: https://github.com/eclipse-ee4j/jaxb-fi/compare/2.0.0...2.1.0