[AIRFLOW-5430] Pin transitive dependency on marshmallow-sqlalchemy
[AIRFLOW-5430] Pin transitive dependency on marshmallow-sqlalchemy

marshmallow-sqlalchemy, a transitive dependency from Flask-AppBuilder,
broke py2 and py35 compatibility with its 0.19.0.

mistercrunch/airflow,apache/airflow,danielvdende/incubator-airflow,wileeam/airflow,nathanielvarona/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,wileeam/airflow,apache/airflow,apache/incubator-airflow,Fokko/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,DinoCow/airflow,danielvdende/incubator-airflow,DinoCow/airflow,mrkm4ntr/incubator-airflow,bolkedebruin/airflow,lyft/incubator-airflow,apache/incubator-airflow,Fokko/incubator-airflow,cfei18/incubator-airflow,wileeam/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,nathanielvarona/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,mtagle/airflow,airbnb/airflow,wooga/airflow,wooga/airflow,sekikn/incubator-airflow,bolkedebruin/airflow,spektom/incubator-airflow,cfei18/incubator-airflow,spektom/incubator-airflow,nathanielvarona/airflow,apache/airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,apache/airflow,Acehaidrey/incubator-airflow,wileeam/airflow,mistercrunch/airflow,dhuang/incubator-airflow,mtagle/airflow,spektom/incubator-airflow,bolkedebruin/airflow,apache/incubator-airflow,lyft/incubator-airflow,Fokko/incubator-airflow,Fokko/incubator-airflow,Acehaidrey/incubator-airflow,mtagle/airflow,dhuang/incubator-airflow,wooga/airflow,apache/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,spektom/incubator-airflow,mistercrunch/airflow,lyft/incubator-airflow,mrkm4ntr/incubator-airflow,cfei18/incubator-airflow,airbnb/airflow,mrkm4ntr/incubator-airflow,lyft/incubator-airflow,airbnb/airflow,apache/airflow,airbnb/airflow,mrkm4ntr/incubator-airflow,sekikn/incubator-airflow,wooga/airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,mtagle/airflow,DinoCow/airflow,DinoCow/airflow,sekikn/incubator-airflow