Add Twitter night mode button

document.getElementById("user-dropdown").getElementsByTagName("ul")[0].innerHTML += `
<li class="dropdown-divider" role="presentation"></li>
<li class="current-user nightmode-toggle" data-name="profile" role="presentation">
    <a class="js-nav" data-nav="view_profile" role="menuitem">
        <span class="DashUserDropdown-linkIcon Icon Icon--medium js-nightmode-icon Icon--crescent">
        </span><span class="js-nightmode-label">Night mode</span>
    </a>
</li>`;