Update mapview.md (react-native-maps#866)

* Update mapview.md

Updated documentation to match the example here (https://github.com/airbnb/react-native-maps/blob/master/example/examples/FitToCoordinates.js)

* Changed name from 'arguments' to 'options'

Author: Diogo do Carmo

docs/mapview.md

@@ -57,7 +57,7 @@
 | `animateToCoordinate` | `region: Coordinate`, `duration: Number` |
 | `fitToElements` | `animated: Boolean` |
 | `fitToSuppliedMarkers` | `markerIDs: String[]` | If you need to use this in `ComponentDidMount`, make sure you put it in a timeout or it will cause performance problems.
-| `fitToCoordinates` | `coordinates: Array<LatLng>, edgePadding: EdgePadding, animated: Boolean` |
+| `fitToCoordinates` | `coordinates: Array<LatLng>, options: { edgePadding: EdgePadding, animated: Boolean }` |