don't require :environment for i18n:check

refs https://trello.com/c/Ls5yeXt4/40

reduces wall time ~20 sec (when not using spring)

test plan:
1. change your database.yml to have a bogus db
2. `rake i18n:check` should not give you a db error
3. `rake i18n:generate` should produce the same yml as before
4. they both should start up about 20 sec faster \o/

Change-Id: I1f13b350f3ccc4d9b572514b5cdaee2f35c02ce4
Reviewed-on: https://gerrit.instructure.com/43887
Product-Review: Jennifer Stern <jstern@instructure.com>
Reviewed-by: Jennifer Stern <jstern@instructure.com>
QA-Review: Jennifer Stern <jstern@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>