Update gunicorn.conf

I changed the command to avoid the error message in gunicorn_err.log (see below).
I changed it according to this example: http://agiliq.com/blog/2014/05/supervisor-with-django-and-gunicorn/

===================================================0
gunicorn_err.log:
!!!
!!! WARNING: This command is deprecated.
!!!
!!!         You should now run your application with the WSGI interface
!!!         installed with your project. Ex.:
!!!
!!!             gunicorn myproject.wsgi:application
!!!
!!!         See https://docs.djangoproject.com/en/1.5/howto/deployment/wsgi/gunicorn/
!!!         for more info.
!!!