Add draggableCursor prop

Adds support for the `draggableCursor` property.

https://developers.google.com/maps/documentation/javascript/reference/map#MapOptions.draggableCursor

Author: Mike Fowler

src/index.js

@@ -156,6 +156,7 @@ export class Map extends React.Component {
           fullscreenControl: this.props.fullscreenControl,
           scrollwheel: this.props.scrollwheel,
           draggable: this.props.draggable,
+          draggableCursor: this.props.draggableCursor,
           keyboardShortcuts: this.props.keyboardShortcuts,
           disableDoubleClickZoom: this.props.disableDoubleClickZoom,
           noClear: this.props.noClear,
@@ -285,6 +286,7 @@ Map.propTypes = {
   fullscreenControl: PropTypes.bool,
   scrollwheel: PropTypes.bool,
   draggable: PropTypes.bool,
+  draggableCursor: PropTypes.string,
   keyboardShortcuts: PropTypes.bool,
   disableDoubleClickZoom: PropTypes.bool,
   noClear: PropTypes.bool,