Must require stringio in newer ruby

[mguthaus]

Using ruby 2.7, I had to add the require statement or I got an error:

ERROR: /home/X/.klayout/ruby/import_tf.rb:71: uninitialized constant TechfileToKLayout::StringIO
/home/X/.klayout/ruby/import_tf.rb:71:in read_skill_file_as_ruby_expr' /home/X/.klayout/ruby/import_tf.rb:196:in import_techfile'
/home/X/.klayout/macros/import_tf_standalone.rb:35:in <module:TechfileToKLayout>' /home/X/.klayout/macros/import_tf_standalone.rb:24:in

' (class NameError)

[Jerry9099]

Thanks so much! I was having the same issue