Fix test failure in Py2.x.

Cython/StringIOTree.py

@@ -30,7 +30,7 @@ EXAMPLE:
 ['first', 'second', 'alpha', 'inserted', 'beta', 'gamma', 'third']
 """
 
-from __future__ import absolute_import, unicode_literals
+from __future__ import absolute_import  #, unicode_literals
 
 try:
     # Prefer cStringIO since io.StringIO() does not support writing 'str' in Py2.