Fix maven 3.2.3 SHA256 checksum

Not sure what happened here, but the checksum has changed.

I've verified the MD5 checksum against http://www.apache.org/dist/maven/maven-3/3.2.3/binaries/apache-maven-3.2.3-bin.tar.gz.md5
Merge branch 'master' of github.com:travis-ci/travis-cookbooks