fix firefox can't entablish websocket.

firefox send websocket upgrade header "Connection:keep-alive, Upgrade" can't match with connection_header_as_str.eq_ignore_ascii_case("upgrade")

Author: mu2019

src/server/mod.rs

@@ -132,7 +132,8 @@ where
             .map(|connection| connection.as_str())
             .unwrap_or("");
 
-        let connection_header_is_upgrade = connection_header_as_str.eq_ignore_ascii_case("upgrade");
+        let connection_header_is_upgrade = connection_header_as_str.split(',')
+            .any(|s| s.trim().eq_ignore_ascii_case("upgrade"));
         let mut close_connection = connection_header_as_str.eq_ignore_ascii_case("close");
 
         let upgrade_requested = has_upgrade_header && connection_header_is_upgrade;