Expose OP_NO_TLSv1_3 (#861)

* Expose OP_NO_TLSv1_3

* Support openssl <1.1.1
diff --git a/doc/api/ssl.rst b/doc/api/ssl.rst
index c678b28..1c09237 100644
--- a/doc/api/ssl.rst
+++ b/doc/api/ssl.rst
@@ -74,6 +74,7 @@
              OP_NO_TLSv1
              OP_NO_TLSv1_1
              OP_NO_TLSv1_2
+             OP_NO_TLSv1_3
 
     Constants used with :py:meth:`set_options` of Context objects.