Repository field in package.json

When running `npm install`, I get the annoying warning:

```
npm WARN package.json execSync@1.0.1-pre No repository field.
```

This can be removed by adding the following to `package.json`:

```
"repository": { 
  "type": "git",
  "url": "http://github.com/mgutz/execSync.git"
}
```
