When you install Aiflow with an extra, the required provider packages should be installed automatically.

For example:

`pip instal apache-airflow[google]` should install apache-airlfow-providers-google package.
setup.py
'simple-salesforce>=1.0.0',
]
samba = [
    'pysmbclient>=0.1.3',
]
segment = [
    'analytics-python>=1.2.9',
]
sendgrid = [
    'sendgrid>=6.0.0,<7',
]
sentry = [
    'blinker>=1.1',
    'sentry-sdk>=0.8.0',
]
singularity = ['spython>=0.0.56']
slack = [
    'slackclient>=2.0.0,<3.0.0',
]
snowflake = [
    'snowflake-connector-python>=1.5.2',
    'snowflake-sqlalchemy>=1.1.0',
]
spark = [
    'pyspark',
]
ssh = [
    'paramiko>=2.6.0',
    'pysftp>=0.2.9',
    'sshtunnel>=0.1.4,<0.2',