Set Twitter message length

Summary:
This change prepares for https://www.theverge.com/2017/9/26/16363912/twitter-character-limit-increase-280-test

Currently, the API refuses statuses > 140 characters, so we can't set it to 280.

Ref T1249.

Test Plan: Fire a longer message than 140 characters.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1249

Differential Revision: https://devcentral.nasqueron.org/D1048