add back essential.js chunk

Author: davidsbailey

apps/Gruntfile.js

@@ -628,6 +628,14 @@ describe('entry tests', () => {
               },
               priority: 10
             },
+            'essential': {
+              name: 'essential',
+              minChunks: 2,
+              chunks: (chunk) => {
+                const chunkNames = ['plc', 'peer_reviews']; // .concat(['code-studio-common'])
+                return chunkNames.includes(chunk.name);
+              },
+            }
           }
         }