title: Yii 2: can not use @web in config/web.php file aliases section
body: <p>I am using basic-template.</p>
  
  <p>here is my code in <code>config/web.php</code>:</p>
  
  <pre><code>return [
      'aliases' =&gt; [
          '@uploadUrl' =&gt; '@web/uploads/',
      ],
  ];
  </code></pre>
  
  <p>I want to use the alias like this: </p>
  
  <pre><code>&lt;?= Html::img( Yii::getAlias('@uploadUrl/'.$model-&gt;image)); ?&gt;
  </code></pre>
  
  <p>But, program erred:</p>
  
  <blockquote>
    <p>Invalid path alias: @web/uploads/</p>
  </blockquote>
  
  <p>thanks for help!</p>