Need support for python 2.6 #609

python-docx is not compatible with python 2.6

From 0.8.8 release of python-docx, seeing below error

Python 2.6.6 (r266:84292, Aug 9 2016, 06:11:56)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-17)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

from docx import Document
Traceback (most recent call last):
File "", line 1, in
File "/usr/lib/python2.6/site-packages/docx/init.py", line 3, in
from docx.api import Document # noqa
File "/usr/lib/python2.6/site-packages/docx/api.py", line 14, in
from docx.package import Package
File "/usr/lib/python2.6/site-packages/docx/package.py", line 9, in
from docx.opc.package import OpcPackage
File "/usr/lib/python2.6/site-packages/docx/opc/package.py", line 116
partnames = {part.partname for part in self.iter_parts()}
^
SyntaxError: invalid syntax