Only install enum34 on python34 and below. (nylas#247)

Small patch to limit `enum34` to installs on Python3.4 or less. Py34 is roughly chosen here due to the relative time of release (w.r.t. the last updates to `enum34`), and to avoid changing deps on any early-adopter py34 projects.

Author: Hooksie

setup.py

@@ -15,8 +15,11 @@
     "requests[security]>=2.4.2",
     "six>=1.4.1",
     "urlobject",
-    "enum34>=1.1.10",
 ]
+
+if sys.version_info[:2] <= (3, 4):
+    RUN_DEPENDENCIES.append("enum34>=1.1.10")
+
 TEST_DEPENDENCIES = [
     "pytest",
     "pytest-cov",