io.c: [DOC] IO#gets [skip ci]

* io.c (rb_io_gets_m): [DOC] fix class name and reword as
  "multibyte".  [Fix rubyGH-1085]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52486 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -3292,8 +3292,8 @@ rb_io_gets(VALUE io)
  *     File.new("testfile").gets   #=> "This is line one\n"
  *     $_                          #=> "This is line one\n"
  *
- *  If StringIO contains characters more than 1 byte
- *  then <code>gets(1)</code> returns character entirely:
+ *  If IO contains multibyte characters byte then <code>gets(1)</code>
+ *  returns character entirely:
  *
  *     # russian characters take 2 bytes
  *     File.write("testfile", "\u{442 435 441 442}")