Change app ID in config.xml

`io.cordova.hello-cordova` isn't permitted as an ID on Android because of the dash. It causes Google's android command-line tool to fail to create a project.
I suspect the same issue would arise on other platforms.

This didn't affect the 2.0.0 release, because nothing is using this config.xml file yet, but it does affect @filmaj's [cordova-client](https://github.com/filmaj/cordova-client) project.

/cc @mwbrooks