[AIRFLOW-4777] Simplify python_requires in setup (#5405)
[AIRFLOW-4777] Simplify python_requires in setup (#5405)

From Airflow 2.0 we support Python 3.5+, but not yet Python 4.0
apache/airflow,cfei18/incubator-airflow,bolkedebruin/airflow,wileeam/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,apache/airflow,wileeam/airflow,DinoCow/airflow,danielvdende/incubator-airflow,mistercrunch/airflow,wooga/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,airbnb/airflow,apache/incubator-airflow,lyft/incubator-airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,mtagle/airflow,mrkm4ntr/incubator-airflow,lyft/incubator-airflow,mistercrunch/airflow,spektom/incubator-airflow,cfei18/incubator-airflow,Fokko/incubator-airflow,DinoCow/airflow,Fokko/incubator-airflow,danielvdende/incubator-airflow,spektom/incubator-airflow,dhuang/incubator-airflow,dhuang/incubator-airflow,wooga/airflow,Fokko/incubator-airflow,mrkm4ntr/incubator-airflow,sekikn/incubator-airflow,mtagle/airflow,DinoCow/airflow,lyft/incubator-airflow,apache/airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,airbnb/airflow,danielvdende/incubator-airflow,wileeam/airflow,nathanielvarona/airflow,apache/airflow,spektom/incubator-airflow,dhuang/incubator-airflow,mrkm4ntr/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,wileeam/airflow,spektom/incubator-airflow,danielvdende/incubator-airflow,mtagle/airflow,bolkedebruin/airflow,apache/airflow,bolkedebruin/airflow,Fokko/incubator-airflow,DinoCow/airflow,airbnb/airflow,wooga/airflow,airbnb/airflow,wooga/airflow,dhuang/incubator-airflow,nathanielvarona/airflow,mtagle/airflow,cfei18/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,apache/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,mrkm4ntr/incubator-airflow