bump selenium-webdriver gem

Change-Id: Ibe4b77daac743f545112985e4afb26cc443f6170
Reviewed-on: https://gerrit.instructure.com/41104
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Shawn Meredith <shawn@instructure.com>
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>