[ruby/irb] fix typo in IRB::Irb#convert_invalid_byte_sequence
IRB::Irb#convert_invalid_byte_sequence
https://github.com/ruby/irb/commit/d09d3c3d68
[ruby/irb] fix typo in
IRB::Irb#convert_invalid_byte_sequencehttps://github.com/ruby/irb/commit/d09d3c3d68