fix(Modal): run close based on prop, not state

Due to setState's async nature, when the modal is opened and closed before setState has finished the modal does not properly cleanup after itself.
Since the init which add the body class is based on props, not state; this change makes the close that cleans up the body class be based on props and not state as well.

fixes #1626

src/Modal.js

@@ -147,7 +147,7 @@ class Modal extends React.Component {
 
     if (this._element) {
       this.destroy();
-      if (this.state.isOpen) {
+      if (this.props.isOpen) {
         this.close();
       }
     }