Spanner bulk load CSV sample not working

## In which file did you encounter the issue?

GoogleCloudPlatform/python-docs-samples/spanner/cloud-client/bulk_load_csv/batch_import.py

### Did you change the file? If so, how?

no

## Describe the issue

Line 76,77

    comments_file = 'hnewscomments.txt'
    stories_file = 'hnewsstories.txt'

It should be ".csv" instead of ".txt"