Remove deprecated Python 3.3 test

See Travis output

Author: szepeviktor

.travis.yml

@@ -2,7 +2,6 @@ language: python
 python:
   - "2.6"
   - "2.7"
-  - "3.3"
   - "3.4"
   - "3.5"
   - "3.6"
@@ -15,4 +14,4 @@ script:
   - tox -e py27 -- -x --integration-tests
 matrix:
   allow_failures:
-  - python: "nightly"
+  - python: "nightly"