Drop Python 3.3 Support (#747)

* Drop Python 3.3 Support

It's reached end-of-life, and our dependencies have started to drop it.
See https://github.com/nvbn/thefuck/pull/744#issuecomment-353244371

* Revert "Use pytest<3.3 to fix Python 3.3 tests (#746)"

This reverts commit f966ecd4f5.

appveyor.yml

@@ -3,7 +3,6 @@ build: false
 environment:
   matrix:
     - PYTHON: "C:/Python27"
-    - PYTHON: "C:/Python33"
     - PYTHON: "C:/Python34"
     - PYTHON: "C:/Python35"
     - PYTHON: "C:/Python36"