npm install fails on scoped modules

[jbeard4]

Steps to reproduce:

1. publish a scoped module to npm-registry-couchapp as an admin user
2. attempt to npm install the scoped module

Expected results: the scoped module should install successfully.
Actual results: the scoped module fails to install with an E404.

I traced this, and the reason is due to the fact that URL to tarballs returned by the show.packages in the design document are not properly escaping the "/" character in the scoped package name.

I believe I have resolved this issue, and will submit a PR. I understand the this project is deprecated and no longer merging PRs, but I wanted to submit this regardless, as it might be useful for someone else.

I would appreciate your feedback. Thank you.