Revert README changes

README.md

@@ -33,7 +33,7 @@ extern crate coap;
 extern crate coap;
 
 use std::io;
-use coap::{CoAPResponse, CoAPRequest};
+use coap::{CoAPServer, CoAPResponse, CoAPRequest};
 
 fn request_handler(req: CoAPRequest) -> Option<CoAPResponse> {
 	println!("Receive request: {:?}", req);