remove support for Python 3.3

Pandas has dropped support for Python 3.3.

We will stop testing Python 3.3 in Travis-CI.

3.4 and newer Python is readily available. There are compatibility
issues with 3.3 related to module "reload" used by Pandas that make it
difficult to continue to support 3.3 along with newer versions of Python.

See also:

pandas-dev/pandas#11273
https://stackoverflow.com/questions/961162/reloading-module-giving-nameerror-name-reload-is-not-defined

Author: danstoner

.travis.yml

@@ -1,7 +1,6 @@
 language: python
 python:
 - '2.7'
-- '3.3'
 - '3.4'
 - '3.5'
 install: