[docs] update image tag typo (#422)

Author: smoreface

src/tags/object/Image.js

@@ -46,7 +46,7 @@ import { guidGenerator } from "../../utils/unique";
  * @param {boolean} [brightnessControl=false] - Show brightness control in toolbar
  * @param {boolean} [contrastControl=false]   - Show contrast control in toolbar
  * @param {boolean} [rotateControl=false]     - Show rotate control in toolbar
- * @param {boolean} [crosshair=false]         – Show crosshair cursor
+ * @param {boolean} [crosshair=false]         - Show crosshair cursor
  */
 const TagAttrs = types.model({
   name: types.identifier,