DOC: specify minimum python version

README_SETUP.md

 # Installation
+python3.6 is required.
 pip install . --user
 pip install tox --user
 

setup.py

@@ -155,6 +155,7 @@ def setup_package():
         author='Timm Fitschen',
         author_email='t.fitschen@indiscale.com',
         packages=find_packages('src'),
+        python_requires='>=3.6',
         package_dir={'': 'src'},
         install_requires=['lxml>=3.6.4',
                           'PyYaml>=3.12', 'future', 'PySocks>=1.6.7'],

tox.ini

 [tox]
-envlist=py34, py35, py36, py37, py38
+envlist=py36, py37, py38
 skip_missing_interpreters = true
 
 [testenv]