allow nested widget previews to update

src/components/Widgets/PreviewHOC.js

@@ -2,7 +2,11 @@ import React from 'react';
 
 class PreviewHOC extends React.Component {
   shouldComponentUpdate(nextProps) {
-    return nextProps.value !== this.props.value;
+    // Only re-render on value change, but always re-render objects and lists.
+    // Their child widgets will each also be wrapped with this component, and
+    // will only be updated on value change.
+    const isWidgetContainer = ['object', 'list'].includes(nextProps.field.get('widget'));
+    return isWidgetContainer || this.props.value !== nextProps.value;
   }
 
   render() {