Declare Python 3.4 as incompatible (#807)

Python 3.4 testing has been dropped in #608, but it was not declared as
incompatible in setup.py because the code base was expected to still
work with Python 3.4 for a while. This compatibility finally broke with
the 21.1.0 release. At least one of the problematic commits is
e09b1d6 introducing an import of
the typing module not available in Python 3.4.

setup.py

@@ -133,7 +133,7 @@ def find_meta(meta):
         long_description_content_type="text/x-rst",
         packages=PACKAGES,
         package_dir={"": "src"},
-        python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*",
+        python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*",
         zip_safe=False,
         classifiers=CLASSIFIERS,
         install_requires=INSTALL_REQUIRES,