Fix assets compilation

Not too sure why the loader behaves differently than it previously did, though.

app/javascript/styles/mastodon/components.scss

@@ -1804,7 +1804,7 @@ a.account__display-name {
   .image-loader__preview-canvas {
     max-width: $media-modal-media-max-width;
     max-height: $media-modal-media-max-height;
-    background: url('../images/void.png') repeat;
+    background: url('~images/void.png') repeat;
     object-fit: contain;
   }
 
@@ -6950,7 +6950,7 @@ noscript {
     width: 100px;
     height: 100px;
     transform: translate(-50%, -50%);
-    background: url('../images/reticle.png') no-repeat 0 0;
+    background: url('~images/reticle.png') no-repeat 0 0;
     border-radius: 50%;
     box-shadow: 0 0 0 9999em rgba($base-shadow-color, 0.35);
   }