remove viewBox attrib and set size(svg_utils issue #1)

gistfile1.py

import matplotlib as pyplot
from lxml import etree

#do some plotting

plt.savefig(fig_file)
width, height = '3.8in', '2.8in'

with file(fig_file, 'r') as fid:
    tree = etree.parse(fid)
root = tree.getroot()
root.attrib.pop('viewBox')
root.attrib['width']=width
root.attrib['height']=height

with file(fig_file, 'w') as fid:
    tree.write(fid, pretty_print=True)