Add food update endpoint

As a user,

I should be able to update a food item in the system by submitting a PATCH request to the endpoint '/api/v1/foods/:id' where :id is the ID of a food item in the system.

The body of the request should be formatted as follows:
```
{
"food": {
"name": "Banana",
"calories": 250
}
}
```
Both the name and calories are required properties for the food item.

If the food item is successfully updated, the response should carry a 200 status code and return the food object formatted as follows:
```
{
"id": 1,
"name": "Banana",
"calories": 250
}
```
If the food item could not be updated, the response should be a 400 status, and include messaging as to why the food item could not be updated:

```
{
"error": "Name is required"
}
```

- [x] Tested
- [x] Documented