Change when menu starts collapsing

Default value couldn't deal with 985 width

static/css/custom-variables.less

@@ -7,3 +7,5 @@
 @navbar-top-background-image: linear-gradient(to bottom, #FFF, #F2F2F2);
 @navbar-top-border: 1px solid #D4D4D4;
 @navbar-top-box-shadow: 0px 1px 10px rgba(0, 0, 0, 0.1);
+
+@grid-float-breakpoint: @screen-md-min;