Switch to using six (#1189)

With the Python 2.7 deadline fast approaching, modernize the codebase
making use of the modernize module to switch to using six, as well as
other upcoming features, such as absolute imports . Stop using 2to3
for Travis, yay!

github/Label.py

@@ -31,11 +31,13 @@
 #                                                                              #
 ################################################################################
 
-import urllib
+from __future__ import absolute_import
+import six.moves.urllib.request, six.moves.urllib.parse, six.moves.urllib.error
 
 import github.GithubObject
 
-import Consts
+from . import Consts
+import six
 
 
 class Label(github.GithubObject.CompletableGithubObject):
@@ -96,9 +98,9 @@ class Label(github.GithubObject.CompletableGithubObject):
         :param description: string
         :rtype: None
         """
-        assert isinstance(name, (str, unicode)), name
-        assert isinstance(color, (str, unicode)), color
-        assert description is github.GithubObject.NotSet or isinstance(description, (str, unicode)), description
+        assert isinstance(name, (str, six.text_type)), name
+        assert isinstance(color, (str, six.text_type)), color
+        assert description is github.GithubObject.NotSet or isinstance(description, (str, six.text_type)), description
         post_parameters = {
             "name": name,
             "color": color,
@@ -115,7 +117,7 @@ class Label(github.GithubObject.CompletableGithubObject):
 
     @property
     def _identity(self):
-        return urllib.quote(self.name)
+        return six.moves.urllib.parse.quote(self.name)
 
     def _initAttributes(self):
         self._color = github.GithubObject.NotSet