Fix broken Font Awesome icons

lms/templates/student_account/login.underscore

@@ -42,7 +42,7 @@
         <% _.each( context.providers, function( provider ) {
             if ( provider.loginUrl ) { %>
                 <button type="button" class="button button-primary button-<%- provider.name %> login-provider login-<%- provider.name %>" data-provider-url="<%- provider.loginUrl %>">
-                    <div class="icon <%- provider.iconClass %>" aria-hidden="true"></div>
+                    <div class="icon fa <%- provider.iconClass %>" aria-hidden="true"></div>
                     <%- provider.name %>
                 </button>
             <% }

lms/templates/student_account/register.underscore

@@ -22,7 +22,7 @@
             _.each( context.providers, function( provider) {
                 if ( provider.registerUrl ) { %>
                     <button type="button" class="button button-primary button-<%- provider.name %> login-provider register-<%- provider.name %>" data-provider-url="<%- provider.registerUrl %>">
-                        <span class="icon <%- provider.iconClass %>" aria-hidden="true"></span>
+                        <span class="icon fa <%- provider.iconClass %>" aria-hidden="true"></span>
                         <%- provider.name %>
                     </button>
             <%  }