spec: enable redis on travis

Change-Id: If25a8372575241a1196bf426b7165bc120fa270a
Reviewed-on: https://gerrit.instructure.com/28712
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>