Replaces directory-copy with ncp

`directory-copy` is not able to handle folders with many files (see test script below). `ncp` looks like a solid alternative.

------

```
var fs = require('fs'),
	copy = require('directory-copy');

try {
	fs.mkdirSync('./test');
} catch(e) {}

try {
	fs.mkdirSync('./test2');
} catch(e) {}

for (var i = 0; i < 1000; i++) {
	fs.writeFileSync('./test/test-' + i, 'a');
}

copy({ src: './test', dest: './test2'}, function (err) {
	console.log(err);
})
```