Remove Python 2.6 support

Not worth including if it poses *any* problems whatsoever

.travis.yml

@@ -1,7 +1,6 @@
 sudo: false
 language: python
 python:
-    - "2.6"
     - "2.7"
     - "3.4"
     - "3.5"

pydiscourse/main.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+
 import cmd
 import json
 import optparse

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26, py27, py34, py35, pypy, pypy3
+envlist = py27, py34, py35, pypy, pypy3
 
 [testenv]
 deps=-rrequirements.dev.txt