Use markers for Python 2-only dependencies.

Author: kdeldycke

CHANGES.rst

@@ -4,7 +4,7 @@ ChangeLog
 `1.5.1 (unreleased) <https://github.com/scaleway/python-scaleway/compare/v1.5.0...develop>`_
 --------------------------------------------------------------------------------------------
 
-* No changes yet.
+* Use markers for Python 2-only dependencies.
 
 
 `1.5.0 (2016-12-19) <https://github.com/scaleway/python-scaleway/compare/v1.4.1...v1.5.0>`_

setup.py

@@ -28,14 +28,11 @@
 
 DEPENDENCIES = [
     'slumber >= 0.6.2',
-    'six']
-
-# Packages required to handle SNI, only for Python2.
-if sys.version_info.major == 2:
-    DEPENDENCIES += [
-        'pyOpenSSL',
-        'ndg-httpsclient',
-        'pyasn1']
+    'six',
+    # Packages required to handle SNI, only for Python2.
+    "pyOpenSSL; python_version < '3.0'",
+    "ndg-httpsclient; python_version < '3.0'",
+    "pyasn; python_version < '3.0'"]
 
 EXTRA_DEPENDENCIES = {
     # Extra dependencies are made available through the