Fix JSON syntax

This PR eliminates duplicate comma syntax errors in package.json.

Before:
```
$ cat | python -mjson.tool
{
    "name": "socket.io-node-client",
  , "version": "0.0.1",
  , "description": "Node.JS Socket.IO client that simulates a variety of browser transports.",
  , "keywords": [],
  , "author": "Guillermo Rauch <guillermo@learnboost.com>",
  , "dependencies": {
      "websocket-client": "1.0.0"
    }
  , "main": "index"
  , "engines": { "node": "0.4.x" }
}
^D
Expecting property name enclosed in double quotes: line 3 column 3 (char 41)
```

After: no error