Update preview less

Author: jhuix

src/less/preview.less

@@ -306,13 +306,13 @@
   }
 
   pre {
-    white-space: pre-wrap;
     /* css-3 */
     white-space: -moz-pre-wrap;
     /* Mozilla, since 1999 */
     white-space: -pre-wrap;
     /* Opera 4-6 */
     white-space: -o-pre-wrap;
+    white-space: pre-wrap;    
     /* Opera 7 */
     word-wrap: break-word;
     /* Internet Explorer 5.5+ */