fix loading css build error

@@ -51,11 +51,11 @@
         > div {
             $init: 0.12s;
 
-            @for $i from 1 to 3 {
-                &:nth-child($i) {
+            @for $i from 1 through 3 {
+                &:nth-child(#{$i}) {
                     animation: loadingScale 0.75s $init infinite cubic-bezier(0.2, 0.68, 0.18, 1.08);
                 }
-                $init: calc(($i + 1) * 0.12);
+                $init: calc((#{$i} + 1) * 0.12);
             }
 
             display: inline-block;