Fixes #26 - Twitter no longer allows since_id of 0
Fixes #26 - Twitter no longer allows since_id of 0

See: https://twittercommunity.com/t/api-v1-1-statuses-user-timeline-since-id-parameter-is-invalid/10202

Seems to fix the issue I'm getting in #26 but I haven't given it extensive testing
emanuel/refme_twitterbot,muffinista/chatterbot,Pirolf/chatterbot