Update your pom.xml file with the following:
<repository>
<snapshots>
<enabled>true</enabled>
</snapshots>
<id>boundless</id>
<name>Boundless Maven Repository</name>
<url>http://repo.boundlessgeo.com/main</url>
</repository>
Using a repository manager allows us to better support "snapshot checksums".
This repository was used for the recent 12-RC1 release, if you find any other jars you would like deployed please give us a shout on the geotools-devel list.
Thanks to Justin, and Boundless, for continued build and release support.