byteslice should be used instead of String#[]

Author: shugo

lib/net/imap/response_parser.rb

@@ -2037,7 +2037,7 @@ def next_token
  return Token.new(T_SPACE, $+)
  elsif $2
  len = $+.to_i
- val = @str[@pos, len]
+ val = @str.byteslice(@pos, len)
  @pos += len
  return Token.new(T_LITERAL8, val)
  elsif $3 && $7
@@ -2068,7 +2068,7 @@ def next_token
  return Token.new(T_RBRA, $+)
  elsif $16
  len = $+.to_i
- val = @str[@pos, len]
+ val = @str.byteslice(@pos, len)
  @pos += len
  return Token.new(T_LITERAL, val)
  elsif $17
@@ -2097,7 +2097,7 @@ def next_token
  return Token.new(T_QUOTED, Patterns.unescape_quoted($+))
  elsif $5
  len = $+.to_i
- val = @str[@pos, len]
+ val = @str.byteslice(@pos, len)
  @pos += len
  return Token.new(T_LITERAL, val)
  elsif $6