spec: fix selenium driver initialization bug

Change-Id: I752f22dd7d9e5448ba885eea9c68ab8dd0ef4d4a
Reviewed-on: https://gerrit.instructure.com/28546
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>