title: bootstrap input group alignment issue
body: <p>Creating a input group in bootstrap 4 but one of the buttons seems to be out of alignment.</p>
  
  <p>here is my code</p>
  
  <pre class="lang-none prettyprint-override"><code>  &lt;div class="col-xs-6 col-sm-6 col-md-6 col-lg-6"&gt;
      &lt;div class="input-group"&gt;
        &lt;input type="text" class="form-control" placeholder="upload file..."&gt;
        &lt;span class="input-group-btn"&gt;
          &lt;label class="btn btn-secondary"&gt;browse&lt;input name="derfile" type="file" style="display: none;"&gt;&lt;/label&gt;
          &lt;button class="btn btn-primary" type="submit"&gt;Submit&lt;/button&gt;
        &lt;/span&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>Here is my <a href="https://jsfiddle.net/0j0gmbjn/" rel="nofollow">fiddle</a></p>
  
  <p>appreciate some assistance</p>