Correct PostgreSQL password in doc example code (#14256)
Correct PostgreSQL password in doc example code (#14256)

The example code block for PostgreSQL sets the password to the ``airflow_user`` instead of ``airflow_pass``.
bolkedebruin/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,apache/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,lyft/incubator-airflow,apache/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,apache/airflow,sekikn/incubator-airflow,sekikn/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,apache/incubator-airflow,apache/airflow,mistercrunch/airflow,apache/incubator-airflow,apache/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/airflow,mistercrunch/airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,lyft/incubator-airflow