bump checkstyle version to build on Java 9 (#3577)
bump checkstyle version to build on Java 9 (#3577)

The version of checkstyle we currently use uses tools.jar
which is removed from Java 9 and above as part of Project Jigsaw.
This commit uses a newer version of checkstyle that does not
use tools.jar.

Running `mvn checkstyle:checkstyle` succeeded.


vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java,vam-google/google-cloud-java