Fixed shell:package task command on Windows systems

[PBartrina]

The extra quotes on the command made the task crash on windows since the quote was added to the path.

[hdeshev]

I think there's a simpler fix for that -- just use double quotes since they work on Windows too. I fixed a similar issue here:

https://github.com/NativeScript/sample-ng-todomvc/blob/master/gruntfile.js#L80

       localInstallModules: {
           command: "npm install \"<%= nsPackagePath %>\""
       },

I'd rather stick with quotes since the command could (in theory) fail if we change the output dir to something that contains spaces.

[PBartrina]

I remember seeing something like c:\pathParent\'pathSon\path' with those single quotes in the middle, that was my reason to try and avoid them, but I see it isn't the solution (nor the case, since it won't show that path in this particular piece of code)
If I see it again, I'll post an issue.

For the moment, I fixed it as you requested, using escaped double quotes.

[hdeshev]

I squashed the commits and merged them manually. Thanks for your contribution!