port 2.3.1 changelog (#4397)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index dc5ec83..350f853 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,6 +8,14 @@
 
 .. note:: This version is not yet released and is under active development.
 
+.. _v2-3-1:
+
+2.3.1 - 2018-08-14
+~~~~~~~~~~~~~~~~~~
+
+* Updated Windows, macOS, and ``manylinux1`` wheels to be compiled with
+  OpenSSL 1.1.0i.
+
 .. _v2-3:
 
 2.3 - 2018-07-18