Разместить ссылки посредине

@media (min-width: 768px) { 
  .nav.navbar-nav { 
    float: none; 
    margin: 0 auto; 
    text-align: center; 
  } 
  .nav.navbar-nav>li { 
    float: none; 
    display: inline-block; 
    vertical-align: middle; 
  }   
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"> 
   
<nav class="navbar navbar-default"> 
  <div class="container"> 
    <!-- Brand and toggle get grouped for better mobile display --> 
    <div class="navbar-header"> 
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false"> 
        <span class="sr-only">Toggle navigation</span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
      </button> 
    </div> 
 
    <!-- Collect the nav links, forms, and other content for toggling --> 
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1"> 
      <ul class="nav  navbar-nav"> 
        <li><a href="#" class="ancLinks">Услуги</a></li> 
        <li><a href="#" class="ancLinks">О нас</a></li> 
        <li><a href="#" class="ancLinks">Отзывы</a></li> 
        <li><a href="#" class="ancLinks">Контакты</a></li> 
      </ul> 
    </div><!-- /.navbar-collapse --> 
  </div><!-- /.container --> 
</nav> 
 
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script> 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

@media (min-width: 768px) { 
  .nav.navbar-nav { 
    width: 100%; 
    display: flex; 
    flex-flow: row nowrap; 
    align-items: center; 
    align-content: center; 
    justify-content: center; 
  } 
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"> 
   
<nav class="navbar navbar-default"> 
  <div class="container"> 
    <!-- Brand and toggle get grouped for better mobile display --> 
    <div class="navbar-header"> 
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false"> 
        <span class="sr-only">Toggle navigation</span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
      </button> 
    </div> 
 
    <!-- Collect the nav links, forms, and other content for toggling --> 
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1"> 
      <ul class="nav  navbar-nav"> 
        <li><a href="#" class="ancLinks">Услуги</a></li> 
        <li><a href="#" class="ancLinks">О нас</a></li> 
        <li><a href="#" class="ancLinks">Отзывы</a></li> 
        <li><a href="#" class="ancLinks">Контакты</a></li> 
      </ul> 
    </div><!-- /.navbar-collapse --> 
  </div><!-- /.container --> 
</nav> 
 
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script> 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

@import url('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css'); 
 
@media (min-width: 768px) { 
  .navbar-nav { 
    float: none; 
  } 
  .navbar-nav > li { 
    text-align: center; 
    width: 25%; 
  }   
}

<nav class="navbar navbar-default"> 
  <div class="container"> 
    <!-- Brand and toggle get grouped for better mobile display --> 
    <div class="navbar-header"> 
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false"> 
        <span class="sr-only">Toggle navigation</span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
        <span class="icon-bar"></span> 
      </button> 
    </div> 
 
    <!-- Collect the nav links, forms, and other content for toggling --> 
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1"> 
      <ul class="nav  navbar-nav"> 
        <li><a href="#" class="ancLinks">Услуги</a></li> 
        <li><a href="#" class="ancLinks">О нас</a></li> 
        <li><a href="#" class="ancLinks">Отзывы</a></li> 
        <li><a href="#" class="ancLinks">Контакты</a></li> 
      </ul> 
    </div><!-- /.navbar-collapse --> 
  </div><!-- /.container --> 
</nav> 
 
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script> 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>