Fix, Update minimum required python version for 2.1.1 in Doc/Instalation (#999)
Fix, Update minimum required python version for 2.1.1 in Doc/Instalation (#999)

* Update minimum supported Python version to 3.6

dpgaspar/Flask-AppBuilder,dpgaspar/Flask-AppBuilder,dpgaspar/Flask-AppBuilder,dpgaspar/Flask-AppBuilder