Fix playground to use new v-model syntax

<template>

  <div style="height: 50vh; width: 50vw;">

    <l-map :zoom="3" :center="[47.41322, -1.219482]" @move="log('move')">

    <l-map

      v-model="zoom"

      v-model:zoom="zoom"

      :center="[47.41322, -1.219482]"

      @move="log('move')"

    >

      <l-tile-layer

        url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"

      ></l-tile-layer>

    LMarker,

    LControlLayers,

  },

  data() {

    return {

      zoom: 2,

    };

  },

  methods: {

    log(a) {

      console.log(a);