Fixing typo in example code

Was spending quite some time figuring out why my app was not receiving any messages... ;-)

fixes #1

package has not been tested in a production app, not yet 1.0

turns out react-native link takes the first file that implements
ReactPackage, so RNThreadPackage must come before BaseReactPackage
alphabetically.  Prefixed it with Thread so RNThreadPackage comes first.