Fix epic show feature spec

HTML rendering doesn't preserve newlines by default, so this is shown as
all one line. Our Markdown rendering also doesn't insert line breaks for
single newlines.

ee/spec/features/epics/epic_show_spec.rb

@@ -42,7 +42,7 @@ describe 'Epic show', :js do
     it 'shows epic title and description' do
       page.within('.epic-page-container .detail-page-description') do
         expect(find('.title-container .title')).to have_content(epic_title)
-        expect(find('.description .md')).to have_content(markdown)
+        expect(find('.description .md')).to have_content(markdown.squish)
       end
     end