Make task-level options as default options in target-level

Hi,
I'd like to use task-level options, but it didn't work, so changed the way of getting options variable.

http://gruntjs.com/api/inside-tasks#this.options

```js
webfont: {
	options:{
		engine:'node'
	},
    production: {
        src: 'icons/*.svg',
        dest: 'build/fonts',
        options: {
            htmlDemo: 'false'
        }
    },
    demo: {
        src: 'icons/*.svg',
        dest: 'build/fonts',
        options: {
            htmlDemo: 'true'
        }
    }
}
```