add 'req' in password authenticate params

some times authentication function need request infomation

I want save req.ip to my log or database when authenticate function called

```
everyauth.password
.authenticate(function (login, password, req) {
  var promise, errors = [];

  // some process like saving successed auth log
  // need req.ip or req.header infomation

  return promise
})
```

very like this reason https://github.com/bnoguchi/everyauth/pull/239

thank you `everyauth`