docs(googlemaps): change observable to promise in main docs (#624)
docs(googlemaps): change observable to promise in main docs (#624)

GoogleMaps.one() returns Promise not Observable
driftyco/ionic-native,xueron/ionic-native,driftyco/ionic-native,ramonornela/ionic-native,xueron/ionic-native,ramonornela/ionic-native,klirix/ionic-native,ramonornela/ionic-native,xueron/ionic-native,driftyco/ionic-native,klirix/ionic-native,klirix/ionic-native,xueron/ionic-native,ramonornela/ionic-native