This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.