Fixed headers on prod (#6123)

cvat-ui/react_nginx.conf

@@ -4,9 +4,9 @@ server {
     location / {
         # Any route that doesn't exist on the server (e.g. /devices)
         try_files $uri $uri/ /index.html;
-        add_header  Cache-Control: "no-cache, no-store, must-revalidate";
-        add_header  Pragma: "no-cache";
-        add_header  Expires: 0;
+        add_header  Cache-Control "no-cache, no-store, must-revalidate";
+        add_header  Pragma "no-cache";
+        add_header  Expires 0;
     }
 
     location /assets {