Exclude versions labeled with -SNAPSHOT from the update check

Maven projects are often labeled with a x.x.x-SNAPSHOT as the version, since they are development builds they shouldn't call the update check.

Additional resource:
Maven documentation (http://maven.apache.org/guides/getting-started/index.html)
"[...] Maven goes a long way to help you with version management and you will often see the SNAPSHOT designator in a version, which indicates that a project is in a state of development. [...]"