Change merge language in maniphest
Summary: Fixes T3467, changes "Merge Duplicates" to "Merge Duplicates In"
Test Plan: Reload Maniphest Page
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T3467
Differential Revision: https://secure.phabricator.com/D6483