increase contrast for copy-course-into-itself warning icon
increase contrast for copy-course-into-itself warning icon

test plan:
 - go to a course's settings / content imports page
 - select "Copy a Canvas Course"
 - search for the course itself
 - the orange exclamation point that appears next to the box
   should meet contrast requirements

fixes ADMIN-996

Change-Id: Ia22590a19d974e737ea3533df89f09f6cb03b897
Reviewed-on: https://gerrit.instructure.com/148625
Tested-by: Jenkins
Reviewed-by: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
QA-Review: Dan Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms