Drop support for Python 3.4, since cryptography dropped it (#884)

diff --git a/setup.py b/setup.py
index 3e76199..e98c41e 100755
--- a/setup.py
+++ b/setup.py
@@ -77,7 +77,6 @@
             'Programming Language :: Python :: 2',
             'Programming Language :: Python :: 2.7',
             'Programming Language :: Python :: 3',
-            'Programming Language :: Python :: 3.4',
             'Programming Language :: Python :: 3.5',
             'Programming Language :: Python :: 3.6',
             'Programming Language :: Python :: 3.7',
@@ -89,6 +88,7 @@
             'Topic :: Software Development :: Libraries :: Python Modules',
             'Topic :: System :: Networking',
         ],
+        python_requires='>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*',
 
         packages=find_packages(where="src"),
         package_dir={"": "src"},