BS v5 buttons update

Updated the display of buttons when used as an `<a>` tag. This change was made in BS4.

mfa/templates/TOTP/Add.html

@@ -98,7 +98,7 @@
                     <button class="btn btn-success" onclick="verify()">Enable</button>
                 </div>
                 <div class="col-md-6" align="right" style="padding-right: 30px">
-                    <a href="{% url 'mfa_home' %}"><button class="btn btn-default">Cancel</button></a>
+                    <a href="{% url 'mfa_home' %}" class="btn btn-default" role="button">Cancel</a>
                 </div>
             </div>
         </div>