Fix type error in Redux Essentials (#3814)

Author: samwightt

docs/tutorials/essentials/part-3-data-flow.md

@@ -121,8 +121,8 @@ We'll import `createSlice`, define our initial posts array, pass that to `create
 import { createSlice } from '@reduxjs/toolkit'
 
 const initialState = [
-  { id: 1, title: 'First Post!', content: 'Hello!' },
-  { id: 2, title: 'Second Post', content: 'More text' }
+  { id: '1', title: 'First Post!', content: 'Hello!' },
+  { id: '2', title: 'Second Post', content: 'More text' }
 ]
 
 const postsSlice = createSlice({

docs/tutorials/essentials/part-4-using-data.md

@@ -55,7 +55,7 @@ export const SinglePostPage = ({ match }) => {
   const { postId } = match.params
 
   const post = useSelector(state =>
-    state.posts.find(post => post.id.toString() === postId)
+    state.posts.find(post => post.id === postId)
   )
 
   if (!post) {