don't export Redis by default

fix #68

Author: linuxmaniac

src/redis.lua

@@ -4,11 +4,6 @@ local redis = {
     _COPYRIGHT   = 'Copyright (C) 2009-2012 Daniele Alessandri',
 }
 
--- The following line is used for backwards compatibility in order to keep the `Redis`
--- global module name. Using `Redis` is now deprecated so you should explicitly assign
--- the module to a local variable when requiring it: `local redis = require('redis')`.
-Redis = redis
-
 local unpack = _G.unpack or table.unpack
 local network, request, response = {}, {}, {}