Dropped python 2.6 support.
Dropped python 2.6 support.

This has been done in order to accept more recent versions of 'unittest' for testing.
Reinaesaya/OUIRL-ChatBot,maclogan/VirtualPenPal,gunthercox/ChatterBot,Reinaesaya/OUIRL-ChatBot,davizucon/ChatterBot,beni55/ChatterBot,vkosuri/ChatterBot,DarkmatterVale/ChatterBot,dgoncalves1/ChatterBot,akfork/ChatterBot,iAmMrinal0/ChatterBot,karajrish/ChatterBot,zan-kusterle/ChatterBot,Gustavo6046/ChatterBot