fixed css

Using `background` instead of `background-image` will override previously set attributes such as `background-repeat: no-repeat` which is indesirable

Author: DRSDavidSoft

lib/ecstatic/show-dir/styles.js

@@ -11,7 +11,7 @@ css += 'td.display-name { padding-left: 1em; }\n';
 
 Object.keys(icons).forEach((key) => {
   css += `i.icon-${key} {\n`;
-  css += `  background: url("data:image/png;base64,${icons[key]}");\n`;
+  css += `  background-image: url("data:image/png;base64,${icons[key]}");\n`;
   css += '}\n\n';
 });