Update python_requires to disable obsolete 3.4 version

[codemrkay]

Description

Due to Python 3.4 is now the highest version of Python, which no longer has official support (3.5 is still supported) and that builds with tests for Pull Requests on Travis are running (for version 3.x) on Python 3.6.7, I changed the requirements for Python: 3.4 is now disabled from acceptable versions.
Official statement from python.org (Python Release Schedule for version 3.4):
"Python 3.4 has now reached its end-of-life and has been retired. No more releases will be made."

Motivation and Context

Pull request according to the #7462 issue ticket about: "Deprecating old versions of Python"

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[CLAassistant]

All committers have signed the CLA.