Allow to pass to constructor config as object

I am creating 'grunt-easymock' library.

I want to pass to constructor config as object .
```
mock = new MockServer({
  port: 3000,
  path: "path/to/dir",
  config: {
    variables: {
      server: "http://example.com"
    },
    routes: [
      "/users/:id"
    ],
  }
});
```

Of course, It can pass to file path.
```
mock = new MockServer({
  port: 3000,
  path: "path/to/dir",
  config: "path/to/config.json"
});
```