title: How to mock modules in storybook's stories?
body: <p>I have a Vue component which includes some external modules with complicated logic. For example:</p>
  <pre class="lang-js prettyprint-override"><code>// Component.vue
  import Vue from 'vue';
  import { externalModule } from '@/path/to/module';
  
  export default {
    methods: {
      useExternalModule() {
        externalModule.doSomethig();
      }
    }
  };
  </code></pre>
  <p>Is it possible to mock the <code>externalModule</code> inside the story?</p>
  <p>I'm using Storybook v6.</p>