Replace .sr-only by .visually-hidden
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mr-auto">
<li class="nav-item active">
- <a class="nav-link" href="{% url 'home' %}">Home <span class="sr-only">(current)</span></a>
+ <a class="nav-link" href="{% url 'home' %}">Home <span class="visually-hidden">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="{% url 'about' %}">About</a>
