fix(dev): Pretty print deltas

internal_packages/worker-ui/lib/developer-bar-long-poll-item.cjsx

@@ -13,7 +13,7 @@ class DeveloperBarLongPollItem extends React.Component
 
   render: =>
     if @state.expanded
-      payload = JSON.stringify(@props.item)
+      payload = JSON.stringify(@props.item, null, 2)
     else
       payload = []
 

internal_packages/worker-ui/stylesheets/worker-ui.less

@@ -170,6 +170,7 @@
         }
 
         .payload {
+          white-space: pre;
           color: burlywood;
         }
       }