update examples/cassandra to api v1beta3

[caesarxuchao]

related: #6584

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[nikhiljindal]

LGTM, thanks!

[thockin]

This is buggy. I ran across it looking at something else. You can't just change the API version and not the calling code. Look 7 lines down - it is trying to decode this object into a v1beta1 structure.

Please audit this and other v1beta3 conversions for this same problem.

[bgrant0607]

@caesarxuchao Did you run the example to ensure that it worked?

[bgrant0607]

The only other URL I found was in rethinkdb, which hasn't been converted yet.

Good catch, thanks.

[caesarxuchao]

I ran through the tutorial, but I didn't check if Cassandra worked properly. I submitted a PR for rethinkdb before I left today. I will ask @nikhiljindal to hold that PR.