improve safari version detection for page view

refs CNVS-9912

test plan:
 * enable page views
 * visit canvas with safari
 * view your page views
 * it should show the safari version number (i.e. 7.0), instead
   of the webkit version number (i.e. 575)

Change-Id: I6f0efcf3c2108fc92accfa86292af1ca7ee6ddaf
Reviewed-on: https://gerrit.instructure.com/34492
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>