Add cgi as a dependency for Ruby 3.5+

Author: andrehjr

split.gemspec

@@ -36,6 +36,7 @@ Gem::Specification.new do |s|
   s.add_dependency "rubystats",       ">= 0.3.0"
   s.add_dependency "matrix"
   s.add_dependency "bigdecimal"
+  s.add_dependency "cgi"
 
   s.add_development_dependency "bundler",     ">= 1.17"
   s.add_development_dependency "simplecov",   "~> 0.15"