fix docs error in to_csv api description
fix docs error in to_csv api description

The header keyword argument is ``header=True`` but was shown as
``with_header=True`` in the short API description.  It's correctly shown
as ``header`` in the long argument description table.

Signed-off-by: Uri Okrent <9568855f4591a8c51ec1e3bd400036cd959899f8@gmail.com>

california-civic-data-coalition/django-postgres-copy