Remove botan.io support

https://github.com/botanio/sdk#this-service-will-be-shut-down-on-25th-may-2018

lib/telegram/bot/client.rb

@@ -9,7 +9,6 @@ module Telegram
       autoload :TypedResponse, 'telegram/bot/client/typed_response'
       extend Initializers
       prepend Async
-      prepend Botan::ClientHelpers
       include DebugClient
 
       require 'telegram/bot/client/api_helper'