[AIRFLOW-XXX] Ignore python files under node_modules in docs (#5063)
[AIRFLOW-XXX] Ignore python files under node_modules in docs (#5063)

Some node modules ship .py files which we don't want in our docs.

Without this change if you attempt to build docs locally on a tree which
you have already compiled the www assets it will fail.
airbnb/airflow,mtagle/airflow,sekikn/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,wileeam/airflow,wileeam/airflow,Fokko/incubator-airflow,sekikn/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,nathanielvarona/airflow,DinoCow/airflow,Fokko/incubator-airflow,Fokko/incubator-airflow,mistercrunch/airflow,airbnb/airflow,apache/airflow,apache/airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,DinoCow/airflow,mistercrunch/airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,mtagle/airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,dhuang/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,wooga/airflow,bolkedebruin/airflow,bolkedebruin/airflow,wooga/airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,DinoCow/airflow,mtagle/airflow,r39132/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,wooga/airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,spektom/incubator-airflow,r39132/airflow,mtagle/airflow,apache/airflow,spektom/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,apache/airflow,r39132/airflow,mrkm4ntr/incubator-airflow,spektom/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,DinoCow/airflow,cfei18/incubator-airflow,lyft/incubator-airflow,wileeam/airflow,apache/airflow,apache/incubator-airflow,r39132/airflow,airbnb/airflow,lyft/incubator-airflow,bolkedebruin/airflow,wileeam/airflow,danielvdende/incubator-airflow,spektom/incubator-airflow,Fokko/incubator-airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,airbnb/airflow,apache/incubator-airflow,wooga/airflow