fonts/unscii: Update to version 2.1

Changelog taken from http://pelulamu.net/unscii/:

In 2020-03-10, the new Unicode version 13.0 added 214 graphics
characters for "legacy computing" (including, among all, the missing
PETSCII characters, and a majority of missing Teletext/Videotex
characters). Most of these were already included in Unscii 1.x, but
now I have been able to give them proper Unicode mappings as
well. This is the main reason for the Unscii 2.0 release.

Additionally, Unscii 2.0 fixes errors in some characters, legibility
in some others and adds a bunch of new ones.

(nikita)