Bumps maven release plugin version from 2.3 to 2.4

I ran into what looks like a bug with 2.3 which is resolved in 2.4:

* http://stackoverflow.com/questions/3291938/maven-release-plugin-ignores-releaseprofile
* http://jira.codehaus.org/browse/MRELEASE-459
* https://issues.apache.org/jira/browse/WINK-125