sguav

On Ubuntu 16.04, `open` is actually [openvt](http://manpages.ubuntu.com/manpages/precise/en/man1/openvt.1.html) which in turn doesn't work for this. Using `xdg-open` should do instead ``` python ... elif platform.system() == 'Linux': call(['xdg-open', pdf_filename], env=ENVIRON) ......