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'