feat(progressbar): new mod added

-mod-progressbar-track-color-white

Author: marissahuysentruyt

components/progressbar/metadata/mods.md

@@ -24,4 +24,5 @@
 | `--mod-progressbar-text-color`                          |
 | `--mod-progressbar-thickness`                           |
 | `--mod-progressbar-track-color`                         |
+| `--mod-progressbar-track-color-white`                   |
 | `--mod-spacing-progressbar-label-to-text`               |