Exception is not raised if day of week is outside of 0-7

```ruby
> CronParser.new("* * * * 100").next
=> 2021-11-01 00:00:00 +0100
```

Other fields seem to raise an exception if the field is out of bound
```ruby
> CronParser.new("100 400 * * *").next
ArgumentError: argument out of range
```