title: BootstapVue b-table: v-if doesnt work with updated item
body: <p>I have an input field in b-table</p>
  <p>template:</p>
  <pre><code>&lt;template v-slot:cell(file)=&quot;data&quot;&gt;
      &lt;b-form-file :state=&quot;Boolean(data.item.file)&quot; @input = 'attachFile(data.item, $event)'&gt;&lt;/b-form-file&gt;
  &lt;/template&gt;
  </code></pre>
  <p>method</p>
  <pre><code>attachFile: function (item, file) {
      item.file = file
  }
  </code></pre>
  <p>But state of b-form-file doesnt change after file attaching. How to fix it?</p>