set server header

or maybe just don't bother adding the server header at all?

http://security.stackexchange.com/questions/23256/what-is-the-http-server-response-header-field-used-for

```
< HTTP/1.1 200 OK
< Date: Sat, 06 Dec 2014 21:22:51 GMT
< version: 6
< type: directory
< path: /
< checksum: 2d33044a
< Content-Length: 516
< Server: Jetty(9.2.z-SNAPSHOT)
```