New error in {nanotime}

I thought {nanotime} was just #297, but after that we see a new error:

```
Error in h(simpleError(msg, call)) : 
  error in evaluating the argument 'x' in selecting a method for function 'as.nanoduration': too many arguments
Calls: <Anonymous> ... seq.nanoduration -> as.nanoduration -> seq -> seq -> seq.integer64
```