CassandraIO uses a non-vendored Guava import

The class CassandraIO.java imports a Guava class but doesn't use the vendored version.

I'm not sure but I think it should use the vendored version. Right?

So:

import com.google.common.base.Joiner;

Should be:

import org.apache.beam.vendor.guava.v20_0.com.google.common.base.Joiner;