Remove trailing whitespace.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

library/HTMLPurifier/AttrTransform/Background.php

@@ -6,17 +6,17 @@
 class HTMLPurifier_AttrTransform_Background extends HTMLPurifier_AttrTransform {
 
     public function transform($attr, $config, $context) {
-        
+
         if (!isset($attr['background'])) return $attr;
-        
+
         $background = $this->confiscateAttr($attr, 'background');
         // some validation should happen here
-        
+
         $this->prependCSS($attr, "background-image:url($background);");
-        
+
         return $attr;
-        
+
     }
-    
+
 }