title: ngx translate angular, how to pass html formatted text to placeholder attribute
body: <p>I have the following problem. 
  My translation key looks like this: </p>
  
  <pre><code>{
    "key": 'Lorem &lt;strong&gt;inpsum&lt;/strong&gt;'
  }
  </code></pre>
  
  <p>and some part of html code:</p>
  
  <pre><code>&lt;form&gt;
    &lt;input [placeholder]="'key | translate'"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Now, how can I pass a key to placeholder if I want to have html formatting?. Currently in my input I can see the text: Lorem &lt; strong > ipsum &lt; /strong >.</p>