student learning mastery: fix truncation of non-paragraphs

test plan:
  * create an outcome
  * for the description, paste in a div of text from another page
  * view the outcome on the student learning mastery page
  * verify that the description is truncated

Change-Id: I6d89fb9e321e16edde2e7be5e65f7ec4af618e70
Reviewed-on: https://gerrit.instructure.com/36571
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
Product-Review: Braden Anderson <braden@instructure.com>