aliases file can now contain functions that need access grunt object

I duplicated a bit of your logic to enable the aliases file to contain function definitions that need access to the grunt object.

As an example, 
```javascript
module.exports = {
  'default': function (grunt) {
    grunt.log.error('This task has been disabled!');
  },
  task1: [
    'thingOne',
    'thingTwo'
  ]
};
```

Due to the simplicity of the change, I did not add a test. You currently have `aliases.yml`, so I didn't want to remove and/or mess with it. With this change, your tests still succeed.