Minor missed tweak on mixins

Author: wndxlori

vendor/assets/stylesheets/bootstrap/_mixins.scss

@@ -446,7 +446,7 @@
   background-image: -o-radial-gradient(circle, $innerColor, $outerColor);
   background-repeat: no-repeat;
 }
-@mixin gradient-striped($color, $angle: 45deg) {
+@mixin gradient-striped($color: #555, $angle: 45deg) {
   background-color: $color;
   background-image: -webkit-gradient(linear, 0 100%, 100% 0, color-stop(.25, rgba(255,255,255,.15)), color-stop(.25, transparent), color-stop(.5, transparent), color-stop(.5, rgba(255,255,255,.15)), color-stop(.75, rgba(255,255,255,.15)), color-stop(.75, transparent), to(transparent));
   background-image: -webkit-linear-gradient($angle, rgba(255,255,255,.15) 25%, transparent 25%, transparent 50%, rgba(255,255,255,.15) 50%, rgba(255,255,255,.15) 75%, transparent 75%, transparent);