* support python39 and delete python35

* support python39 in Dockerfile.centos

* fix ubuntu18 bug

* update Dockerfile.ubuntu setuptools

* fix centos py39 errors

* fix centos py39 error2

* update develop whl package name

* distingush cpu and gpu name

* fix ref_gcc

* change whl name

* upgrade gcc 4.8 to 5.4 in ubuntu_dev

* update gcc4.8 to 5.4 in centos

* Upgrade pip from 18.0 to 20.0.1

* change 2.1.0_dev0 to 2.1.0.dev0 in gpu version

* clean dockerfile

* clean dockerfile