Add factory girl

Converts tests to use factory girl
Here you're depending on the food truck to have an ID of 1. Rather you can implicitly create the food truck when you create the review if you have the above association added:

```ruby
review = FactoryGirl.create(:review) # This will create a FoodTruck record as well.

visit food_truck_path(review.food_truck)

expect(page).to have_content(review.rating)
expect(page).to have_content(review.body)
```