fix: pass custom options to arrow modifier (#116)

Author: langovoi

src/Popper.jsx

@@ -117,6 +117,7 @@ class Popper extends Component {
     }
     if (this._arrowNode) {
       modifiers.arrow = {
+        ...(this.props.modifiers.arrow || {}),
         element: this._arrowNode,
       }
     }