Fix dancing-ruby Ctrl+C stop

[tompng]

IRB has an easter egg

$ irb --noautocomplete
irb(main):001> RubyVM[PRESS TAB KEY]
easter egg ([:logo and :dancing] two patterns randomly)

Since reline 0.3.3, dancing ruby easter egg does not stop with CTRL+C because STDOUT is raw mode. I added STDOUT.cooked do end
(I think it's from ruby/reline#474, reline stopped changing raw-mode and cooked mode frequently while rendering)

Stopping dancing-ruby with CTRL+C will abort input to IRB.

if true
  RubyVM[PRESS TAB KEY] [CTRL+C] # The input `if true\n  RUBYVM` is cleared

To avoid it, I also added trap("SIGINT")

[st0012]

Thanks 👍