Remove reference to `this`

Remove reference to `this` so that Faker.Internet.email and domainName can be used without having to bind the function receiver with `Faker.Internet.email.bind(Faker.Internet)`.

Before:

```
var factory = require('factory-girl'),
    User = require('src/models/User');
factory.define('User', User, {
  given_name: Faker.Name.firstName,
  surname: Faker.Name.lastName,
  email: Faker.Internet.email.bind(Faker.Internet)
});
```

After:

```
var factory = require('factory-girl'),
    User = require('src/models/User');
factory.define('User', User, {
  given_name: Faker.Name.firstName,
  surname: Faker.Name.lastName,
  email: Faker.Internet.email
});
```

Unfortunately this doesn't play nice with your build step. Happy to make any changes if you've got a suggestion for how you'd like that to be handled.