connect: fix typo in result string of prot_name()

Replace 'unkown' with 'unknown'.
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

connect.c

@@ -254,7 +254,7 @@ static const char *prot_name(enum protocol protocol)
 		case PROTO_GIT:
 			return "git";
 		default:
-			return "unkown protocol";
+			return "unknown protocol";
 	}
 }