Fixed nonceCheck type conversion bug

This was causing TTLs a *bit* longer than 60 seconds... around 4351.15 years actually. :laughing: 

@rfk remedial js http://wtfjs.com/

```js
assert.equal("12345" + 60, "1234560")
assert.equal(+"12345" + 60, 12405)
assert.equal("1234560" - 60, 1234500)
assert.equal("12345" * 1000, 12345000)
```

see also #426