add second argument `context` to reduce function shape (#22)
add second argument `context` to reduce function shape (#22)

so the signature of a plug using 'apply.reduce' is now:

```js
(value, context) => nextValue
```

with `context` being passed in to the top function call.

related to: https://github.com/bendrucker/value-pipe/pull/2
depject/depject,dominictarr/depject