Error Stack option

Hi, at the moment if I have an error in my server or any dependent file, the error has the following format:
```sh
Running "express-server:livereload:/var/folders/h7/hlgn4tkx017900b50c3slndh0000gn/T/express11385-3407-bt8fld/livereload.server" (express-server) task
Fatal error: Server ["/Users/tim/Dropbox/code/express-angular-test/server"] -  
ReferenceError: expors is not defined
```

In my example, the error came from a file, the main server requires. It is not possible to debug here.
My suggestion is to add a `showStack` option to enable the full error stack.
If the option is default to `true` or `false` is your decision, but I would at least offer the feature.

Thanks,
Tim Suchanek