Using dash "-" to define stdout not working

**Issue by [TheDeadCode](https://github.com/TheDeadCode)**
_Saturday Aug 05, 2017 at 18:08 GMT_
_Originally opened as https://github.com/gsscoder/commandline/issues/466_

----

A bit like wget where you can do `wget https://someurl -O -` to say to output to stdout.
Although I cannot get it to work:

```
./generator.exe -o -

ERROR(S):
Option 'o, output' has no value.
Required option 'o, output' is missing.
```