enhance Typescript comment

modules/store/src/action_creator.ts

@@ -26,8 +26,15 @@ export function createAction<
     [key: string]: any;
   }
 >(type: T, payload?: P) {
-  // Spread types may only be created from object types. ts(2698) Typescript 3.1.1
-  // const action = payload === undefined ? { type } : { type, ...payload };
+  /*
+  The following line requires Typescript 3.2: Generic spread expressions in
+  object literals. 
+  https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-2.html
+  
+  Typescript 3.1.1 gives error: Spread types may only be created from 
+  object types. ts(2698) 
+  */
+  // const action = payload === undefined ?{ type } : { type, ...payload };
   const action =
     payload === undefined ? { type } : { type, ...(payload as object) };
   return action;