fix the example dvr config file error

@@ -7,7 +7,7 @@ max_connections     1000;
 vhost __defaultVhost__ {
     dvr {
         enabled      on;
-        dvr_path     dvr_path     ./objs/nginx/html/[app]/[stream].[timestamp].flv;
+        dvr_path     ./objs/nginx/html/[app]/[stream].[timestamp].flv;
         dvr_plan     session;
     }
 }