Better wording for ie8-is-not-supported page

fixes: CNVS-12521

test plan:

go to canvas in IE 6, 7, or 8.
you should see this: http://cl.ly/image/3D1g0C1e1X45

Change-Id: Ic7f630b076a21331a0d005e94cbaba03f068ed24
Reviewed-on: https://gerrit.instructure.com/33532
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>