.navbar-nav li a::before {
    content: ' ';
    display: block;
    width: 1px;
    height: 70%;
    background: #fff;
    position: absolute;
    bottom: 15%; /* it makes me center */
    left: 0;
}

/* uncomment if you want to hide first stripe
.navbar-nav li:first-child a::before {
    display: none;
}
*/