Add minimum version of pylint (#14775)
Add minimum version of pylint (#14775)

We are using some pylint rules that were added in pylint 2.7.0,
for example `consider-using-generator`. When older version of
pylint is used, it fails with this error:

* E0012: Bad option value 'consider-using-generator' (bad-option-value)

Adding lower-limit forces the pylint to be upgraded even if
someone's image or installation already had pylint installed.
apache/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,apache/incubator-airflow,apache/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,apache/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,apache/airflow,bolkedebruin/airflow,bolkedebruin/airflow