add data-key attribute to Text component

lib/components/text.js

@@ -43,8 +43,9 @@ class Text extends React.Component {
    */
 
   render() {
+    const { node } = this.props
     return (
-      <span>
+      <span data-key={node.key}>
         {this.renderLeaves()}
       </span>
     )