nano: update to 2.9.4

2018.03.08 - GNU nano 2.9.4 "Isabel" allows binding a key to a string
            (any piece of text and/or commands), permits customizing
            the color of error messages with 'set errorcolor', colors
            those error messages by default in bright white on red,
            makes <Enter> at the bottom of the screen scroll just one
            row when --smooth is used, does not fail when redoing a
            file insertion, and cancels a Shift-selection when any
            cursor key is pressed without Shift even when the cursor
            cannot move.  Further, it treats tabs fully the same as
            spaces when doing automatic hard-wrapping, allows syntax
            names to be unquoted, and removes two deprecated options
            and six deprecated bindable function names.

(wiedi)