title: 'tab' is not a known element errors when adding ng2-bootstrap to angular2-seed
body: <p>I am trying to add <strong>ng2-bootstrap</strong> into a <em>fresh clone</em> of the <strong>angular2-seed</strong> project, but I keep getting the following error (or similar):</p>
  
  <pre><code>Unhandled Promise rejection: Template parse errors: 'tab' is not a known element
  </code></pre>
  
  <p>I have followed the instructions <a href="https://github.com/mgechev/angular2-seed/wiki/Add-external-dependency" rel="noreferrer">here</a> and tried several variations, but it just doesn't want to work. I have it working in other projects that use different versions of angular2-seed, so perhaps something has changed that isn't documented in their wiki yet.</p>
  
  <p>I have created a repo demonstrating my problem: <a href="https://github.com/danielcrisp/angular2-seed" rel="noreferrer">https://github.com/danielcrisp/angular2-seed</a></p>
  
  <p>As I said it is a fresh clone of angular2-seed, with the following changes:</p>
  
  <p><code>$ npm install ng2-bootstrap --save</code></p>
  
  <p>Then update the config:</p>
  
  <pre><code>this.SYSTEM_CONFIG_DEV.paths['ng2-bootstrap'] =
    `${this.APP_BASE}node_modules/ng2-bootstrap/ng2-bootstrap.js`;
  
  this.SYSTEM_BUILDER_CONFIG.packages['ng2-bootstrap'] = {
      main: 'ng2-bootstrap.js',
      defaultExtension : 'js'
  };
  </code></pre>
  
  <p>Import <code>Ng2BootstrapModule</code> into the <code>NgModule</code>.</p>
  
  <p>And then I added some tabs to test.</p>
  
  <pre><code>&lt;tabset&gt;
    &lt;tab&gt;1&lt;/tab&gt;
    &lt;tab&gt;2&lt;/tab&gt;
  &lt;/tabset&gt;
  </code></pre>
  
  <p>If I remove the tabs from the HTML I get no errors. I also get errors if I try other ng2-bootstrap components, e.g. </p>
  
  <pre><code>&lt;button type="button" class="btn btn-primary" [(ngModel)]="singleModel" btnCheckbox btnCheckboxTrue="1" btnCheckboxFalse="0"&gt;`
  </code></pre>