Progress bar height attribute should be in the wrapper

[Tubo]

Hi, thanks for the awesome package.

The progress bar current does not render height options properly.

According to Bootstrap Doc, the height style should be set on .progress rather than on .progress-bar.

<div class="progress" style="height: 1px;">
  <div class="progress-bar" role="progressbar" style="width: 25%;" aria-valuenow="25" aria-valuemin="0" aria-valuemax="100"></div>
</div>

Currently, elm-bootstrap render like this:

<div class="progress">
  <div class="progress-bar" role="progressbar" style="width: 25%; height: 1px;" aria-valuenow="25" aria-valuemin="0" aria-valuemax="100"></div>
</div>

It therefore incorrectly renders to:

Thanks!