Well, the length of the menu is quite long. You could try to decrease font sizes or remove unneeded menu items. You can also remove any extra space added by the Donut theme by following these steps:
1. Edit file Donut-theme/css/donut.min.css
2. Add these lines at the end of the file:
@media (min-width:768px){
.navbar-nav>li{margin-left:8px}
.navbar-nav>li>a{padding: 10px 0;line-height:30px}
}
.navbar .logo-wrapper {height: 35px}
.nav.navbar-nav.navbar-right.login-nav, .nav.navbar-nav.navbar-right.notf-bubble, .nav.navbar-nav.navbar-right.user-nav {padding: 4px 0}
header#nav-header {min-height: 55px}
3. Clear your browser's cache (In Chrome, press F12 and then CTRL+SHIFT+R)