[SPARKR][MINOR] Fix example of spark.naiveBayes

## What changes were proposed in this pull request?

The original example doesn't work because the features are not categorical. This PR fixes this by changing to another dataset.

## How was this patch tested?

Manual test.

Author: Junyang Qian <junyangq@databricks.com>

Closes #14820 from junyangq/SPARK-FixNaiveBayes.