问Bootstrap -修改折叠导航栏宽度阈值？(使用Gem)

EN

$navbarCollapseWidth: 850px;
@import "bootstrap";

$grid-float-breakpoint: 850px;
@import "bootstrap";

<nav class="navbar navbar-default" role="navigation">
  <div class="container-fluid">
    <!-- Brand and toggle get grouped for better mobile display -->
    <div class="navbar-header">
      <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
        <span class="sr-only">Toggle navigation</span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Site Name</a>
    </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><%= link_to "Home", root_path %></li>
        <li><%= link_to "About", about_path %></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown">Rules<b class="caret"></b></a>
            <ul class="dropdown-menu">
              <% @awards.each do |award| %>
                <li><%= link_to award.name, award %></li>
              <% end %>
            </ul>
        </li>
        <li><%= link_to "How to Submit", instructions_path %></li>
        <li><%= link_to "Contact Us", contact_path %></li>
      </ul>
      <ul class="nav navbar-nav navbar-right">
        <% if signed_in? %>
          <li><%= link_to "My Submissions", submissions_path %></li>
          <li class="dropdown">
            <a href="#" class="dropdown-toggle" data-toggle="dropdown">My Account<b class="caret"></b></a>
            <ul class="dropdown-menu">
              <li><%= link_to "Account Profile", user_path(current_user.id) %></li>
              <li><%= link_to "Change Password", edit_user_registration_path %></li>
              <% if current_user.admin? == true %>
                <li class="divider"></li>
                <li><%= link_to "Admin Dashboard", admin_root_path %></li>
              <% end %>
              <% if current_user.judge? == true %>
                <li class="divider"></li>
                <li><%= link_to "Judge Dashboard", scores_path %></li>
              <% end %>
              <li class="divider"></li>
              <li><%= link_to "Sign Out", destroy_user_session_path, method: :delete %></li>
            </ul>
          </li>
        <% else %>
          <li><%= link_to "Create an Account", new_user_registration_path %></li>
          <li><%= link_to "Sign In", new_user_session_path %></li>
        <% end %>
      </ul>
    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>