svgwrite missing in virtualenv installation instructions

[CassioPimentel]

ERROR:
Traceback (most recent call last):
File "/usr/local/bin/simplecv", line 9, in
load_entry_point('SimpleCV==1.3', 'console_scripts', 'simplecv')()
File "/usr/lib/python2.6/dist-packages/pkg_resources.py", line 299, in load_entry_point
return get_distribution(dist).load_entry_point(group, name)
File "/usr/lib/python2.6/dist-packages/pkg_resources.py", line 2229, in load_entry_point
return ep.load()
File "/usr/lib/python2.6/dist-packages/pkg_resources.py", line 1948, in load
entry = import(self.module_name, globals(),globals(), ['name'])
File "/usr/local/lib/python2.6/dist-packages/SimpleCV-1.3-py2.6.egg/SimpleCV/init.py", line 4, in
from SimpleCV.Camera import *
File "/usr/local/lib/python2.6/dist-packages/SimpleCV-1.3-py2.6.egg/SimpleCV/Camera.py", line 5, in
from SimpleCV.ImageClass import Image, ImageSet, ColorSpace
File "/usr/local/lib/python2.6/dist-packages/SimpleCV-1.3-py2.6.egg/SimpleCV/ImageClass.py", line 14768, in
from SimpleCV.DrawingLayer import *
File "/usr/local/lib/python2.6/dist-packages/SimpleCV-1.3-py2.6.egg/SimpleCV/DrawingLayer.py", line 5, in
import svgwrite
File "/usr/local/lib/python2.6/dist-packages/svgwrite/init.py", line 51, in
from svgwrite.drawing import Drawing
File "/usr/local/lib/python2.6/dist-packages/svgwrite/drawing.py", line 29, in
from svgwrite.container import SVG, Defs
File "/usr/local/lib/python2.6/dist-packages/svgwrite/container.py", line 27, in
from svgwrite.base import BaseElement
File "/usr/local/lib/python2.6/dist-packages/svgwrite/base.py", line 12, in
from svgwrite.etree import etree
File "/usr/local/lib/python2.6/dist-packages/svgwrite/etree.py", line 33, in
original_serialize_xml = etree._serialize_xml
AttributeError: 'module' object has no attribute '_serialize_xml'