title: ion-content won't show when using Ionic core 4
body: <p>I'm developing an app that uses Vue.js and Ionic, but I can't figure it out why updating my Ionic core version breaks the ion-content tag, I tried googling if the tag was discontinued, but it doesn't seem to be the case.</p>
  
  <p>To illustrate, I've made a example that uses Ionic core. With the latest Ionic version the ion-content tag doesn't show up, but if you switch to the older Ionic version, then it shows just fine.</p>
  
  <pre><code>&lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Ionic Test&lt;/title&gt;
      &lt;script src="https://unpkg.com/@ionic/core@latest/dist/ionic.js"&gt;&lt;/script&gt;
      &lt;!-- &lt;script src="https://unpkg.com/@ionic/core@0.0.2-30/dist/ionic.js"&gt;&lt;/script&gt; --&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;ion-app&gt;
          &lt;ion-page&gt;
          &lt;ion-header&gt;
              &lt;ion-toolbar&gt;
              &lt;ion-title&gt;Example&lt;/ion-title&gt;
              &lt;/ion-toolbar&gt;
          &lt;/ion-header&gt;
          &lt;ion-content class="content" padding&gt;
              &lt;ion-list&gt;
                  &lt;/ion-item&gt;
                      &lt;ion-label full&gt;I'm an example text...&lt;/ion-label&gt;
                      &lt;ion-button&gt;Example button&lt;/ion-button&gt;
                  &lt;/ion-item&gt;
              &lt;/ion-list&gt;
          &lt;/ion-content&gt;
          &lt;/ion-page&gt;
      &lt;/ion-app&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p>Here's a jsFiddle for this code: <a href="https://jsfiddle.net/telmo/chk9h080/" rel="nofollow noreferrer">https://jsfiddle.net/telmo/chk9h080/</a></p>
  
  <p>Can someone explain to me what is happening here?</p>