Log Message:
nudoku: update to 2.1.0.

ChangeLog:

2.0.0 to 2.1.0 (2020-11-20)
  * Use actual terminal background color (instead of black) as background
  color (pr #31)
  * Define minimum gettext version instead of exact one (pr #32)
  * Require gettext 0.20
  * Add Japanese translation (pr #40)
  * Minor code change