add key to repeated element

Author: contactashish13

classes/Visualizer/Gutenberg/build/block.js

@@ -124,7 +124,7 @@ class Charts extends Component {
 										}
 
 										return (
-											<div className="visualizer-settings__charts-single">
+											<div className="visualizer-settings__charts-single" key={ `chart-${ charts[i].id }` }>
 
 												<div className="visualizer-settings__charts-title">
 													{ title }