Increase character count for Tweet text

[adityanag]

The DB schema is set to 140 chars for the tweet text. However, this is no longer true - see https://blog.twitter.com/official/en_us/a/express-even-more-in-140-characters.html

Many tweets are getting truncated because of this. I'd recommend raising the limit to ~300 or something like that; still small, but big enough to get all the text.

Thanks!