fix: Center Throbber circles (#198)

Author: tassoevan

packages/fuselage/.loki/reference/chrome_iphone7_Misc_Throbber_Default.png

@@ -30,7 +30,6 @@ export const Throbber = forwardRef(function Throbber({
 }, ref) {
   return <Box
     componentClassName='rcx-throbber'
-    is='div'
     ref={ref}
     {...props}
   >

packages/fuselage/.loki/reference/chrome_iphone7_Misc_Throbber_Disabled.png

@@ -2,6 +2,7 @@
   display: flex;
 
   margin-block: calc(-1 * #{ $spaces-x1 });
+  justify-content: center;
 
   &__circle {
     margin-inline: $spaces-x1;