Removed a couple old ruby 1.8 hacks (#456)

Author: andrew

lib/split/extensions.rb

@@ -1,4 +1,4 @@
 # frozen_string_literal: true
-%w[array string].each do |f|
+%w[string].each do |f|
   require "split/extensions/#{f}"
 end

lib/split/extensions/array.rb

@@ -10,7 +10,6 @@
 require 'split'
 require 'ostruct'
 require 'yaml'
-require 'complex' if RUBY_VERSION.match(/1\.8/)
 
 Dir['./spec/support/*.rb'].each { |f| require f }