Fix intention and add missing payload extraction (#79)

Author: christoph-jerolimov

docs/api/createReducer.md

@@ -84,14 +84,15 @@ const todosReducer = createReducer([], {
   [addTodo]: (state, action) => {
     // This push() operation gets translated into the same
     // extended-array creation as in the previous example.
-	  state.push(todo)
+    const todo = action.payload
+    state.push(todo)
   },
   [toggleTodo]: (state, action) => {
     // The "mutating" version of this case reducer is much
     //  more direct than the explicitly pure one.
     const index = action.payload
-	  const todo = state[index]
-	  todo.completed = !todo.completed
+    const todo = state[index]
+    todo.completed = !todo.completed
   }
 })
 ```