Fixes LinusU#12

Migration guide:

While verifiers generated with an earlier version of this library will continue to work, the client and the server must either both be using the padding, or both not.

The recommended upgrade path is to have both versions running on your server, which gives you time to upgrade all the clients. This can be accomplished by depending on this library two times:

```js
{
  // ...
  "dependencies": {
    // ...
    "secure-remote-password": "^0.4.0",
    "secure-remote-password-pre-rfc5054": "LinusU/secure-remote-password#pre-rfc5054"
  }
}
```

You will then have to implement another version of your endpoint, which uses the newer version.

```js
const loginCtrl1 = require('./controller/login-v1')
const loginCtrl2 = require('./controller/login-v2')

app.post('/v1/login-sessions', loginCtrl1.initiate)
app.post('/v1/login-sessions/:sessionId/finalize', loginCtrl1.finalize)

app.post('/v2/login-sessions', loginCtrl2.initiate)
app.post('/v2/login-sessions/:sessionId/finalize', loginCtrl2.finalize)
```

The `login-v1` controller should import the library as such:

```js
require('secure-remote-password-pre-rfc5054/server')
```

The `login-v2` controller should import the library as usual:

```js
require('secure-remote-password/server')
```