fix: adding new line before key header

this is to stop other headers ending in Sec-WebSocket-Key from breaking the index of

source/Server/ServerHandshake.cs

@@ -15,7 +15,7 @@ internal class ServerHandshake
         const int ResponseLength = 129;
         internal const int KeyLength = 24;
         const int MergedKeyLength = 60;
-        const string KeyHeaderString = "Sec-WebSocket-Key: ";
+        const string KeyHeaderString = "\r\nSec-WebSocket-Key: ";
         // this isn't an official max, just a reasonable size for a websocket handshake
         readonly int maxHttpHeaderSize = 3000;