Errors and warnings on a simple Vue.js powered page

Hello,

I just started a course on Udemy about Vue.js, that is new to me: just from the start, in a simple page like the following, I get lot of errors and warnings (of course I installed and activated the official Vue plugin):

<div id="app">
    <input type="text" v-on:input="changeTitle">
    <p>{{ title }}</p>
</div>

<script>
    new Vue({
        el: '#app',
        data: {
            title: 'Hello world!'
        },
        methods: {
            changeTitle: function(event){
                this.title = event.target.value;
            }
        }
    });
</script>

1. on v-on: "Namespace 'v-on' is not bound"
2. on changeTitle into methods: "Unused property changeTitle"

What's wrong with this simple snippet? If warning and errors come on this very simple snippet, I don't wanaìna think what will happen in most complex scripts...

Please any help?