Merge pull request #1258 from blink1073/add-install-requires

FIX: Restore six to install_requires

setup.py

@@ -141,6 +141,9 @@ if __name__ == "__main__":
         ],
 
         configuration=configuration,
+        install_requires=[
+            "six>=%s" % DEPENDENCIES['six']
+        ],
         packages=setuptools.find_packages(exclude=['doc']),
         include_package_data=True,
         zip_safe=False,  # the package can run out of an .egg file