Merge pull request #456 from h2o/kazuho/ech-emit-config_id

provide API to obtain ECH config_id being used
diff --git a/include/picotls.h b/include/picotls.h
index 60fc7ed..9762dad 100644
--- a/include/picotls.h
+++ b/include/picotls.h
@@ -135,7 +135,7 @@
 
 /* negotiated_groups */
 #define PTLS_GROUP_SECP256R1 23
-#define PTLS_GROUP_NAME_SECP256R1 "scep256r1"
+#define PTLS_GROUP_NAME_SECP256R1 "secp256r1"
 #define PTLS_GROUP_SECP384R1 24
 #define PTLS_GROUP_NAME_SECP384R1 "secp384r1"
 #define PTLS_GROUP_SECP521R1 25