Changed setup.py check from using six to sys

Bumped requirements for youtube-dl and websocket-client

requirements.txt

@@ -2,4 +2,4 @@ gevent==1.2.2
 holster==2.0.0
 requests==2.18.4
 six==1.11.0
-websocket-client==0.44.0
+websocket-client==0.46.0

setup.py

@@ -1,4 +1,4 @@
-import six
+import sys
 from setuptools import setup, find_packages
 
 from disco import VERSION
@@ -13,8 +13,8 @@ extras_require = {
     'voice': ['pynacl==1.2.1'],
     'http': ['flask==0.12.2'],
     'yaml': ['pyyaml==3.12'],
-    'music': ['youtube_dl>=2017.12.2'],
-    'performance': ['erlpack==0.3.2' if six.PY2 else 'earl-etf==2.1.2', 'ujson==1.35'],
+    'music': ['youtube_dl>=2017.12.31'],
+    'performance': ['erlpack==0.3.2' if sys.version_info.major == 2 else 'earl-etf==2.1.2', 'ujson==1.35'],
     'sharding': ['gipc==0.6.0'],
     'docs': ['biblio==0.0.4'],
 }