Use absolute paths for new working/not-found SVGs

This allows these component styles to be used in i.e. the win95 skin.

app/javascript/styles/mastodon/components.scss

@@ -2323,7 +2323,7 @@
   }
 
   &__figure {
-    background: url('../images/elephant_ui_working.svg') no-repeat center 0;
+    background: url('~images/elephant_ui_working.svg') no-repeat center 0;
     width: 100%;
     height: 160px;
     background-size: contain;
@@ -2337,7 +2337,7 @@
     padding-top: 20px + 48px;
 
     .regeneration-indicator__figure {
-      background-image: url('../images/elephant_ui_disappointed.svg');
+      background-image: url('~images/elephant_ui_disappointed.svg');
     }
   }