fixes #5163: add new var for navbar collapse's default view, use that in responsive navbar css

less/responsive-navbar.less

@@ -166,7 +166,7 @@
 // DEFAULT DESKTOP
 // ---------------
 
-@media (min-width: 980px) {
+@media (min-width: @navbarCollapseDesktopWidth) {
 
   // Required to make the collapsing navbar work on regular desktops
   .nav-collapse.collapse {

less/variables.less

@@ -157,6 +157,7 @@
 // Navbar
 // -------------------------
 @navbarCollapseWidth:             979px;
+@navbarCollapseDesktopWidth:      @navbarCollapseWidth + 1;
 
 @navbarHeight:                    40px;
 @navbarBackgroundHighlight:       #ffffff;