We should not use a hard path in cache bust

web/includes/functions.php

@@ -2064,7 +2064,7 @@ function cache_bust( $file ) {
   $dirname = preg_replace( '/\//', '_', $parts['dirname'] );
   $cacheFile = $dirname.'_'.$parts['filename'].'-'.$css.'-'.filemtime($file).'.'.$parts['extension'];
   if ( file_exists(ZM_DIR_CACHE.'/'.$cacheFile) or symlink(ZM_PATH_WEB.'/'.$file, ZM_DIR_CACHE.'/'.$cacheFile) ) {
-    return '/zm/cache/'.$cacheFile;
+    return 'cache/'.$cacheFile;
   } else {
     Warning("Failed linking $file to $cacheFile");
   }