Update references to the extended master secret draft.

It's now an RFC too.

Change-Id: I2aa7a862bf51ff01215455e87b16f259fc468490
Reviewed-on: https://boringssl-review.googlesource.com/7028
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index decf5fc..c010d7f 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -933,7 +933,7 @@
 
 /* Extended Master Secret.
  *
- * https://tools.ietf.org/html/draft-ietf-tls-session-hash-05 */
+ * https://tools.ietf.org/html/rfc7627 */
 
 static void ext_ems_init(SSL *ssl) {
   ssl->s3->tmp.extended_master_secret = 0;