fix(geolocation): fix watchPosition return type
fix(geolocation): fix watchPosition return type

closes #741

ramonornela/ionic-native,ramonornela/ionic-native,xueron/ionic-native,ramonornela/ionic-native,driftyco/ionic-native,klirix/ionic-native,driftyco/ionic-native,xueron/ionic-native,driftyco/ionic-native,klirix/ionic-native,klirix/ionic-native,xueron/ionic-native,xueron/ionic-native,ramonornela/ionic-native