Remove support for python 3.4
The series 3.4 will be retired on March 17,so we should no more support it for next release: https://www.python.org/dev/peps/pep-0429/
The series 3.4 will be retired on March 17,so we should no more support it for next release: https://www.python.org/dev/peps/pep-0429/