[ruby/irb] Use 0.step instead of (..0).each for Ruby 2.5

https://github.com/ruby/irb/commit/5d628ca40e

lib/irb/easter-egg.rb

@@ -116,7 +116,7 @@ module IRB
           end
           ruby_model = RubyModel.new
           print "\e[?1049h"
-          (0..).each do |i|
+          0.step do |i| # TODO (0..).each needs Ruby 2.6 or later
             buff = canvas.draw do
               ruby_model.render_frame(i) do |p1, p2|
                 canvas.line(p1, p2)