Fixes TypeError: __init__() takes exactly 2 arguments bug.
Fixes TypeError: __init__() takes exactly 2 arguments bug.

The problem was that webob released v1.1.1 which removed the
`header_name` parameter from Accept.__init__. See:
https://bitbucket.org/ianb/webob/changeset/0b6029a2cda7
Thus, conneg.py is updated to not use `header_name`.

zacharyvoase/dagny