Quick fix for safari 'node not found' bug

Summary:
This is a quick fix, but we will do a follow-up diff to add more precautions
and fix any other misnamed refs. Want to push this asap to fix the bug.

In a previous diff[1] we changed the syntax for getting the reference to the
editor node, but this spot was not updated.
[1]: https://our.intern.facebook.com/intern/diff/D5964582/

This introduced a bug where clicking a link caused the focus to move but the
selection state was not cleared, and this is a known issue in Safari in
particular. In the past we had a work-around in Draft, but the work-around was
no longer working due to the misnamed ref.

PS Thanks to @[578934877:sophiebits] for pairing with me and realizing the root cause of the bug. :)

Reviewed By: sophiebits

Differential Revision: D6344247

fbshipit-source-id: fb0c3f2a7264fc68319536d6c18c30a27053c0aa

Author: flarnie

src/component/handlers/edit/editOnBlur.js

@@ -31,7 +31,7 @@ function editOnBlur(editor: DraftEditor, e: SyntheticEvent<>): void {
   // opposed to clicking to another tab or window).
   if (getActiveElement() === document.body) {
     const selection = global.getSelection();
-    const editorNode = editor.refs.editor;
+    const editorNode = editor.editor;
     if (
       selection.rangeCount === 1 &&
       containsNode(editorNode, selection.anchorNode) &&