fix(MdBottomBarItem): missing props to for router link

[VdustR]

Fix missing props to for vue router link after $attrs changed.

$attrs is read only, so I think replace it with a new computed attrs is better.

Notice that the props to would be always sent via props, therefore there will be no html attribute to on <a> anymore.

fix #1412

My test case:

<template>
  <div>
    <md-checkbox v-model="funcPresent">test</md-checkbox>
    <md-bottom-bar md-type="shift" class="md-layout md-alignment-center-center md-primary" md-sync-route>
      <md-bottom-bar-item to="/components/bottom-bar/123" md-icon="home" md-label="Home" class="md-layout-item">
      </md-bottom-bar-item>
      <md-bottom-bar-item v-if="funcPresent" to="/components/bottom-bar/func" md-icon="lightbulb_outline" md-label="Func" class="md-layout-item"> </md-bottom-bar-item>
    </md-bottom-bar>
  </div>
</template>

<script>
  export default {
    name: 'BarRouter',

    data () {
      return {
        funcPresent: false
      }
    }
  }

</script>

<style lang="scss" scoped>
  .phone-viewport {
    width: 322px;
    height: 200px;
    display: inline-flex;
    align-items: flex-end;
    overflow: hidden;
    border: 1px solid rgba(#000, .26);
    background: rgba(#000, .06);
  }

</style>

[marcosmoura]

This is the same thing for tabs too. Can you change the tabs as well? I will merge this one and, if possible, you can create another PR :D

[VdustR]

I think there is no similar bug with MdTab.

vue-material/src/components/MdTabs/MdTab.vue

Line 57 in 156506b

props: this.getPropValues(),