title: Apache Airflow 1.9 install on debian 8 from GitHub
body: <p>I installed Apache airflow 1.9 from GitHub thanks to this command line on debian 9: <code>pip install git+https://github.com/apache/incubator-airflow.git@v1-9-stable</code></p>
  
  <p>However, I have an error during the <code>airflow initdb</code> caused by Fernet, do you know how to solve this issue?</p>
  
  <pre><code>   INFO  [alembic.runtime.migration] Running upgrade 947454bf1dff -&gt; d2ae31099d61, Increase text size for MySQL (not relevant for other DBs' text types)
      [2017-12-27 17:19:24,586] {models.py:643} ERROR - Failed to load fernet while encrypting value, using non-encrypted value.
      Traceback (most recent call last):
        File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 639, in set_extra
          fernet = get_fernet()
        File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 103, in get_fernet
          raise AirflowException('Failed to import Fernet, it may not be installed')
      AirflowException: Failed to import Fernet, it may not be installed
      [2017-12-27 17:19:24,601] {models.py:643} ERROR - Failed to load fernet 
  </code></pre>
  
  <p>And how can I specify extrapackage like in <code>pip install apache-airflow[gcp-api]</code> from my previous pip command install with GitHub?</p>
  
  <p>How to install the latest 1.9.0RC too? I have an assertionError.</p>