Drop py33 (#677)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index af2f26d..7b2f4db 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -12,7 +12,8 @@
 Backward-incompatible changes:
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-*none*
+- Dropped support for Python 3.3.
+  `#677 <https://github.com/pyca/pyopenssl/pull/677>`_
 
 
 Deprecations: