Drop support for end-of-life Python versions

Per the [dev
guide](https://docs.python.org/devguide/#status-of-python-branches), the
following versions have been end of lifed:

- 2.6: 2013-10-29
- 3.1: 2012-04-11
- 3.2: 2016-02-20

Removing support for EOL versions should make future maintenance easier.

.travis.yml

@@ -1,6 +1,5 @@
 language: python
 python:
-- '2.6'
 - '2.7'
 - '3.3'
 - '3.4'

setup.py

@@ -43,8 +43,6 @@
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.1',
-        'Programming Language :: Python :: 3.2',
         'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
     ]

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = flake8,py26,py27,py35
+envlist = flake8,py27,py35
 
 [flake8]
 ; E501: line too long (X > 79 characters)