wildfly-parent.pom: upgrade Jackson to 1.9.12 to be consistent with RESTEasy 3.0.1.Final

https://repository.jboss.org/nexus/content/groups/public/org/wildfly/wildfly-parent/8.0.0.Alpha1/wildfly-parent-8.0.0.Alpha1.pom specifies version 1.9.9 for Jackson being used in RESTEasy. However,
https://repository.jboss.org/nexus/content/groups/public/org/jboss/resteasy/resteasy-jaxrs-all/3.0.1.Final/resteasy-jaxrs-all-3.0.1.Final.pom specifies version 1.9.12.

BTW, even RESTEasy 3.0-beta-4 contains Jackson 1.9.10, and not 1.9.9 being part of the current WildFly snapshot.