Request descriptor's payload/meta functions not passed the parsed action

It looks like the request type descriptors' payload and meta functions are being passed the raw, top-level RSAA as the action argument, instead of an action with parsed values.

For instance, if we take the example from the README:

// Input RSAA
{
  [RSAA]: {
    endpoint: 'http://www.example.com/api/users',
    method: 'GET',
    types: [
      {
        type: 'REQUEST',
        payload: (action, state) => ({ endpoint: action.endpoint })
      },
      'SUCCESS',
      'FAILURE'
    ]
  }
}

The documentation implies that the above RSAA action should result in the following FSA request action being dispatched:

// expected…
{
  type: 'REQUEST',
  payload: { endpoint: 'http://www.example.com/api/users' },
}

Instead, the dispatched FSA request action has an empty object as it's payload:

// actual…
{
  type: 'REQUEST',
  payload: {  },
}

Cause

This is because the payload function is being passed the unparsed, top-level RSAA action here:

// We can now dispatch the request FSA
if (
  typeof requestType.payload === 'function' ||
  typeof requestType.meta === 'function'
) {
  //          top-level [RSAA] action ⌄⌄⌄⌄⌄⌄
  next(await actionWith(requestType, [action, getState()]));
} else {
  next(requestType);
}

Based on the docs, I was expecting the following:

// We can now dispatch the request FSA
if (
  typeof requestType.payload === 'function' ||
  typeof requestType.meta === 'function'
) {
  const parsedAction = {
    ...action[RSAA],
    method,
    body,
    headers,
  };
  next(await actionWith(requestType, [parsedAction, getState()]));
} else {
  next(requestType);
}

This behavior appears in both the master and next branches.

I'd be happy to submit a PR, if this is indeed a bug.