py33 is finally too old; remove it

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index c805571..e14bfa5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,6 @@
 matrix:
   include:
     - python: 2.7
-    - python: 3.3
     - python: 3.4
     - python: 3.5
     - python: 3.6

CHANGELOG.rst

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index e4a8b4b..17dfb5c 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -4,7 +4,7 @@
 2.0.31 (unreleased)
 -------------------
 
-- Nothing changed yet.
+- py33 is no longer supported. It may works but has been removed from tox config
 
 
 2.0.30 (2018-06-23)

tox.ini

diff --git a/tox.ini b/tox.ini
index 0dc70c8..7757aa2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 skip_missing_interpreters=true
-envlist=py27,py33,py34,py35,py36,py37,coverage
+envlist=py27,py34,py35,py36,py37,coverage
 
 [testenv]
 skip_install=true