hotfix: start script [windows]

Hi, here is a hotfix for the windows issue, when `options.command` is not specified. Then `execPath` is taken, but `process.execPath` can contain spaces, like `C:\Program Files (x86)\nodejs\node.exe`, so we have then not a valid command after `split(/\s+/)` in `trySpawn`.  

I would say, it is a hotfix, as it would be better to take the command parsing out from the `trySpawn` and do this in constructor.

Cheers, Alex.