fix #239

[ashidaharo]

fix #239

note: In order to create this fix, 
      I also looked at lib/nodist.js for reference, which is supposed to handle "latest" as well, 
      and found out that they use lib/version.js to handle versions. 
      Unlike lib/nodist/js, lib/npm.js has to deal with "match", 
      so it seems to have its own version handling defined.
      Following the philosophy that if you don't need to make a big change, you shouldn't, 
      I've limited myself to a small fix to npm.js. 
      But I'm curious, so I'll make a special note here.

[ashidaharo]

Is there a problem?