Hi,
the ncursesw-sup gem has been yanked from rubygems. The gems are still
available for download if you really need it:
https://rubygems.org/gems/ncursesw-sup
note that the gem namespace is now free for someone else to take over, so
I do not recommend doing that.
The ncursesw-sup gem is replaced by the ncursesw gem which the newest
sup 0.15.2 depends on.
Regards, Gaute