Install enum34 only on Python < 3.4

Author: Henry Chan

setup.py

@@ -34,8 +34,8 @@
     packages=find_packages(exclude=["tests*",]),
     zip_safe=False,
     license=about["__license__"],
-    install_requires=["enum34>=1.1.10", "requests>=2.22.0"],
-    extras_require={"dev": dev_requirements,},
+    install_requires=["requests>=2.22.0"],
+    extras_require={"dev": dev_requirements, ":python_version<'3.4'": ["enum34"],},
     classifiers=[
         "Development Status :: 1 - Planning",
         "Intended Audience :: Developers",