Fix pty.js dep

The latest versioned Pty is broken for anyone using node pre v0.11.x
https://github.com/chjj/pty.js/commit/18238d37e2915b3ac97e4ae0d5cb3e33f76ac758

This fixes the problem since they are not doing a release
Merge pull request #30 from samccone/master

Fix pty.js dep