use $navbar-breakpoints in generation loop

Signed-off-by: pine3ree <pine3ree@gmail.com>

Author: pine3ree

scss/_navbar.scss

@@ -191,8 +191,8 @@
 // where your navbar collapses.
 .navbar-expand {
   @each $breakpoint in map-keys($navbar-breakpoints) {
-    $next: breakpoint-next($breakpoint, $grid-breakpoints);
-    $infix: breakpoint-infix($next, $grid-breakpoints);
+    $next: breakpoint-next($breakpoint, $navbar-breakpoints);
+    $infix: breakpoint-infix($next, $navbar-breakpoints);
 
     // stylelint-disable-next-line scss/selector-no-union-class-name
     &#{$infix} {