Refactor box-shadow style for sidebar to satisfy css lint

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/framework/sidebar.scss

@@ -17,7 +17,7 @@
     height: 100%;
     overflow: hidden;
     transition: width $sidebar-transition-duration;
-    @include box-shadow(2px 0px 16px 0px #bbb);
+    @include box-shadow(2px 0 16px 0 #bbb);
   }
 }