[NEW] Import StringIO para python 2 e 3

pynfe/utils/__init__.py

@@ -10,7 +10,10 @@ try:
 except ImportError:
     raise Exception('Falhou ao importar lxml/ElementTree')
 
-from io import StringIO
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
 
 try:
     from . import flags