allow 'better_file_browsing' feature flag in prod

this makes it so the 'better_file_browsing' feature
is no longer 'hidden' in prodcution

Change-Id: I138c9c1ee77d53b91e2fac2244c7c91e298a2b26
Reviewed-on: https://gerrit.instructure.com/43943
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>
Reviewed-by: Dan Minkevitch <dan@instructure.com>