Substitua a tag button pelo codigo abaixo:
<button class="navbar-toggle collapsed" type="button" data-toggle="collapse" data-target="#collapse-navbar" aria-controls="collapse-navbar" aria-expanded="false" aria-label="Toggle navigation">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
