fs.statSync used in async version of fs-finder

Could you please change it to asynchronous?

``` javascript
function Base(directory) {
//...
  if (!fs.statSync(directory).isDirectory()) {
   throw new Error("Path " + directory + " is not directory");
  }
//...
}
```

``` javascript
fs.stat(directory,function(err,stat){
   if(err || !stat.isDirectory()) {
      throw new Error("Path " + directory + " is not directory");
    }
});
```
