update default http cache config

conf/autoload_configs/http_cache.conf.xml

@@ -3,6 +3,8 @@
     <param name="max-urls" value="10000"/>
     <param name="location" value="$${base_dir}/http_cache"/>
     <param name="default-max-age" value="86400"/>
+    <param name="prefetch-thread-count" value="8"/>
+    <param name="prefetch-queue-size" value="100"/>
   </settings>
 </configuration>