Fix typo's on python_requires in setup.py

setup.py

@@ -108,7 +108,7 @@ setup(name=name,
         'Topic :: Office/Business',
         ],
     license='GPL-3',
-    python_required='>=3.4',
+    python_requires='>=3.4',
     install_requires=requires,
     dependency_links=dependency_links,
     zip_safe=False,