Update finch variation study name.

The same feature flag is controlled by two different studies, depending
on which version of Chrome is being used. Update the study name to refer
to the current version's study, now that M57 has gone to stable.


Review-Url: https://codereview.chromium.org/2762583002
Cr-Commit-Position: refs/heads/master@{#458269}
1 file changed