fix(reset): Property name for styled scrollbars (#9210)

https://webplatform.news/issues/2018-10-26

app/javascript/styles/mastodon/reset.scss

@@ -54,8 +54,7 @@ table {
 }
 
 html {
-  scrollbar-face-color: lighten($ui-base-color, 4%);
-  scrollbar-track-color: rgba($base-overlay-background, 0.1);
+  scrollbar-color: lighten($ui-base-color, 4%) transparent;
 }
 
 ::-webkit-scrollbar {