Added version info on package.json

Added version info on package.json
npm install crashed without version info.

Here is the log:
```
npm install
npm ERR! install Couldn't read dependencies
npm ERR! Error: no version
npm ERR!     at validVersion (/usr/local/lib/node_modules/npm/node_modules/read-package-json/read-json.js:580:32)
```