persist the blur event so clients can use it

Author: triptate

src/Mentions.tsx

@@ -243,6 +243,11 @@ class Mentions extends React.Component<MentionsProps, MentionsState> {
   };
 
   public onBlur = (event?: React.FocusEvent<HTMLTextAreaElement>) => {
+    // the timeout causes onBlur to be called async, which causes the react synthetic
+    // event to be nullified. persist it if possible so clients can use it.
+    if (event.persist) {
+      event.persist();
+    }
     this.focusId = window.setTimeout(() => {
       const { onBlur } = this.props;
       this.setState({ isFocus: false });