Fixed Dropdown height for small lists
Fixed Dropdown height for small lists

By using a fixed `height` for the Dropdown module, you get an ugly list when the number of items is small, since the end of the list is empty.
By changing it to `height` to `maxHeight`, RN can easily reduce the size if the list is too small.
sohobloo/react-native-modal-dropdown,sohobloo/react-native-modal-dropdown,sohobloo/react-native-modal-dropdown