[BUG] Encoding command-line parameter

[Paul-Wassermann-CA]

Description

Specifying an --enc argument results in an error (see below). Therefore, the encoding used to read / write files cannot be changed.

To repoduce :

Call python -m licenseheaders --enc utf8 -f

An error is raised : TypeError: open() argument 'encoding' must be str or None, not list

How to fix the bug

See https://github.com/johann-petrak/licenseheaders/blob/master/licenseheaders.py#L412 for reference. The add_argument method for the "--enc" parameter should be called without specifying nargs, as specifying it results in the encoding being wrappend in a list (even for nargs=1).