Add python_requires for >= 3.4

setup.py

@@ -9,6 +9,7 @@ setup(name='pyHS100',
       license='GPLv3',
       packages=['pyHS100'],
       install_requires=['click', 'click-datetime', 'typing'],
+      python_requires='>=3.4',
       entry_points={
             'console_scripts': [
                   'pyhs100=pyHS100.cli:cli',