Enable TLS 1.3 by default.

Update-Note: If calling code does not work with TLS 1.3, the simplest
fix is to call SSL_CTX_set_max_proto_version(ctx, TLS1_2_VERSION).

Change-Id: Ic99861753dac117c52aea1988a6c4227a32984ca
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/38624
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/ssl/ssl_versions.cc b/ssl/ssl_versions.cc
index e63a189..d95aeb3 100644
--- a/ssl/ssl_versions.cc
+++ b/ssl/ssl_versions.cc
@@ -150,7 +150,7 @@
                             uint16_t version) {
   // Zero is interpreted as the default maximum version.
   if (version == 0) {
-    *out = method->is_dtls ? DTLS1_2_VERSION : TLS1_2_VERSION;
+    *out = method->is_dtls ? DTLS1_2_VERSION : TLS1_3_VERSION;
     return true;
   }