Fixed scroller bar with google chrome.

Fixed the scroll bar on the outcomes screen for google chrome
users running yosemite.

fixes CNVS-16903

test plan:
- Create a course and go to the outcomes screen.
- Create an outcome and scroll within the outcome.
- Edit an outcome and try to scroll within the outcome.
- Create and outcome with long description and scroll
  within the outcome pane.
- Do this for all browsers.

Change-Id: Icd4ce4d038bbd14ea18f675bcb02e039fd032390
Reviewed-on: https://gerrit.instructure.com/44747
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Matt Berns <mberns@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>