switch to 0 based indexing

the world rocked for a moment (and more fixes to follow)
also the crumbling of idealism was heard

test/parfait/test_integer.rb

@@ -39,7 +39,7 @@ module Parfait
       20.times do
         assert int
         assert_equal Parfait::Integer , int.class
-        assert int.get_internal_word(2)
+        assert int.get_internal_word(1)
         int = int.next_integer
       end
     end