fixed twitter page iteration problem in chapter 1

Hello,

First thanks a lot for your book, which is very interesting and useful. 

I think I found an issue in the notebook for chapter 1. In my case, the loop was always stopping after the second iteration, because the next_results field is not set anymore by the twitter API. So I could not get more than 200 tweets, for any query. 
I found out that we can use the max_id field instead, which is always set properly. 

Cheers, 

Colin