fix typo in better file browsing description

closes #CNVS-14324

Change-Id: I492c8aaae22556f3f332eb3c924db28b08ccfef3
Reviewed-on: https://gerrit.instructure.com/37860
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>