Update TodoList.vue

[jakubdomanski]

126-128 = Support for the Firefox browser without polyfill (Firefox do not support event as global).

Proposition :

    //line 72-80
    if (this.filter == 'all') {
        return this.todos
      } else if (this.filter == 'active') {
        return this.todos.filter(todo => !todo.completed)
      } else if (this.filter == 'completed') {
        return this.todos.filter(todo => todo.completed)
      }
      
      return this.todos

You are returning the same thing with first if and last return the if do not make sense.
This should look like that :

     if (this.filter == 'active') {
        return this.todos.filter(todo => !todo.completed)
      } else if (this.filter == 'completed') {
        return this.todos.filter(todo => todo.completed)
      }
      
      return this.todos

But personally, I'd use switch over if's, just like this :

  switch (this.filter){
    case 'active':
      return this.todos.filter( todo => !todo.completed )
    case 'completed':
      return this.todos.filter( todo => todo.completed )
    }

    return this.todos //still not sure if this should have default return when all we know all cases

Cheers,
Jakub