title: S3Hook in Airflow: no attribute 'get_credentials'
body: <p>I am using s3_to_reshift_operator at <a href="https://github.com/apache/incubator-airflow/blob/master/airflow/operators/s3_to_redshift_operator.py" rel="nofollow noreferrer">https://github.com/apache/incubator-airflow/blob/master/airflow/operators/s3_to_redshift_operator.py</a> and got the following error when I executed it:</p>
  
  <pre><code>AttributeError: 'S3Hook' object has no attribute 'get_credentials'
  </code></pre>
  
  <p>It looks like underlying S3Hook being used in my environment is different from one used in the repo. How can I get around this? I tried to upgrade Airflow but it didn't resolve my problem.</p>