drop support for TLS 1.3 draft versions
diff --git a/lib/picotls.c b/lib/picotls.c
index 7dd75ba..88a6e64 100644
--- a/lib/picotls.c
+++ b/lib/picotls.c
@@ -66,10 +66,7 @@
 #define PTLS_EXTENSION_TYPE_KEY_SHARE 51
 #define PTLS_EXTENSION_TYPE_ENCRYPTED_SERVER_NAME 0xffce
 
-#define PTLS_PROTOCOL_VERSION_TLS13_FINAL 0x0304
-#define PTLS_PROTOCOL_VERSION_TLS13_DRAFT26 0x7f1a
-#define PTLS_PROTOCOL_VERSION_TLS13_DRAFT27 0x7f1b
-#define PTLS_PROTOCOL_VERSION_TLS13_DRAFT28 0x7f1c
+#define PTLS_PROTOCOL_VERSION_TLS13 0x0304
 
 #define PTLS_SERVER_NAME_TYPE_HOSTNAME 0
 
@@ -115,8 +112,7 @@
 /**
  * list of supported versions in the preferred order
  */
-static const uint16_t supported_versions[] = {PTLS_PROTOCOL_VERSION_TLS13_FINAL, PTLS_PROTOCOL_VERSION_TLS13_DRAFT28,
-                                              PTLS_PROTOCOL_VERSION_TLS13_DRAFT27, PTLS_PROTOCOL_VERSION_TLS13_DRAFT26};
+static const uint16_t supported_versions[] = {PTLS_PROTOCOL_VERSION_TLS13};
 
 static const uint8_t hello_retry_random[PTLS_HELLO_RANDOM_SIZE] = {0xCF, 0x21, 0xAD, 0x74, 0xE5, 0x9A, 0x61, 0x11, 0xBE, 0x1D, 0x8C,
                                                                    0x02, 0x1E, 0x65, 0xB8, 0x91, 0xC2, 0xA2, 0x11, 0x16, 0x7A, 0xBB,