Add Header::DATE

The "Date" header, should be send with responses.

http/src/header.rs

@@ -322,6 +322,7 @@ impl HeaderName<'static> {
     // NOTE: we adding here also add to the
     // `functional::header::from_str_known_headers` test.
     known_headers!(
+        4: [ (DATE, "date") ],
         5: [ (ALLOW, "allow") ],
         10: [ (USER_AGENT, "user-agent") ],
         12: [ (X_REQUEST_ID, "x-request-id") ],

http/tests/functional/header.rs

@@ -127,6 +127,7 @@ fn parse_header() {
 #[test]
 fn from_str_known_headers() {
     let known_headers = &[
+        "date",
         "allow",
         "user-agent",
         "x-request-id",