fixed quotation marks in version

the quotation marks were in unicode instead of plain ascii and caused an error:
```
>python setup.py install
  File "setup.py", line 47
SyntaxError: Non-ASCII character '\xe2' in file setup.py on line 47, but no encoding declared; see http://python.org/dev/peps/pep-0263/ for details
```
with my fix, it now works.