a usage sample in StringJoiner b73 spec needs update

[Dmitry Bessonov]

Currently an example in the spec for StringJoiner class:
http://jre.us.oracle.com/java/re/lambda/8/promoted/ea/b73/docs/api/java/util/StringJoiner.html
still contains usage of Stream.into() method.

       List people = ...
       String commaSeparatedNames =
           people.map( p -> p.getName() )
               .into( new StringJoiner(", ") )
               .toString();


-Dmitry