Replacing map with filter in an example

[kopeczech]

---

name: 📝 Documentation Fix
about: A small fix in an example code

What docs page needs to be fixed?

• Section: Using Redux
• Page: Deriving Data with Selectors

What is the problem?

Example code snippet uses the map method in a place where filter method should be used instead.

function TodoList() {
  // highlight-start
  // ❌ WARNING: this _always_ returns a new reference, so it will _always_ re-render!
  const completedTodos = useSelector(state =>
    state.todos.map(todo => todo.completed)
  )
  // highlight-end
}

What changes does this PR make to fix the problem?

map has been replaced with filter

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[EskiMojo14]

thanks!