Merge pull request #20 from fchapoton/patch-1

do not use six

Author: vbraun

setup.py

@@ -8,7 +8,6 @@
     author='Volker Braun',
     author_email='[email protected]',
     install_requires=[
-        'six',
         'ipython>=4',
         'nbconvert>=4',
         'notebook',

test/test_sagenb_reader.py

@@ -1,17 +1,16 @@
 
 import os
 import unittest
-import six
 from sagenb_export.sagenb_reader import (
     NotebookSageNB,
     TextCell, ComputeCell,
 )
 
 
-if six.PY2:
-    string_type = unicode
-else:
-    string_type = str
+try:
+    string_type = unicode  # py2
+except NameError:
+    string_type = str  # py3
 
 
 DOT_SAGE = os.path.join(os.path.dirname(__file__), 'dot_sage')