fix links to nightly docs and specification

 * nightly docs are here: http://scala-lang.org/files/archive/nightly/2.11.x/api/2.11.x/

   the old link points to some pre-2.11.0 nightly.
 * specification is now here: http://scala-lang.org/files/archive/spec/2.11/
Looks like this should also link to Sec. 6.24 (I know no Japanese, but I'm guessing you're modifying parallel sections).