MDL Slider - valueNumber missing setter

[ntoljic]

When I add a slider to my Vue component as shown in the docs I get the following
warning:

Computed property "valueNumber" was assigned to but it has no setter.

Sample component:

<template lang="pug">
    mdl-slider(v-model="amount" min="0" max="100")
</template>

<script lang="ts">
import {Component, Vue} from 'vue-property-decorator';

@Component
export default class SliderComponent extends Vue {
  private amount: number = 5;
}
</script>

A quick look into slider.vue shows that valueNumber indeed only has a getter defined like so:

valueNumber () {
  return Number(this.value)
},

From a quick google search it is my understanding that if a computed property is used with v-model, as is the case with valueNumber, it must have a corresponding setter.

Therefore my suggested fix is to simply add a setter for valueNumber.