Update setup.py to make it Python3 compatible.

In Python3 print has been changed from a statement to a function; for this reason, commands like "print 'ciao'" will not work anymore, and will have to be replaced by commands like "print('ciao')".

Please, accept this change since at the moment doing a "pip install fonttools" works while "pip3 install fonttools" does not work.
Thank you for your work!