Update cause sentence for builds used to test snapshots.
Update cause sentence for builds used to test snapshots.

Test Plan: Manually verified on local Changes instance

Reviewers: haoyi, kylec

Reviewed By: kylec

Subscribers: changesbot

Differential Revision: https://tails.corp.dropbox.com/D149407

dropbox/changes,dropbox/changes,dropbox/changes,dropbox/changes