I define the timer in each my-progress, used to update the value of view, but the console shows the value of the constant changes, and the value of view is still not changed, how can I do in the timer to change the value of view

Vue.component('my-progress', {

    template: '

            <div class=progress progress-bar-vertical data-toggle=tooltip data-placement=top>

                <div class=progress-bar role=progressbar aria-valuenow=0 aria-valuemin=0 aria-valuemax=100 :style={height: pgvalue}>{{pgvalue}}

                </div>

            </div>

        ',

    data : function(){  



        return {

            pgvalue : '50%',

            intervalid1:'',

        }

    },

    computed:{



        changes : {

            get : function(){

                return this.pgvalue;

            },

            set : function(v){

                this.pgvalue =  v;

            }

        }

    },

    mounted : function(){



        this.todo()     

    },

    beforeDestroy () {



       clearInterval(this.intervalid1)

    },

    methods : {



        todo : function(){          

            this.intervalid1 = setInterval(function(){

                this.changes = ((Math.random() * 100).toFixed(2))+'%';

                console.log (this.changes);

            }, 3000);

        }

    },

})

here is the link:
jsbin.com/safolom