fix display of FIMB quiz questions on rails 3

fixes CNVS-13790

string manipulation just lost the html_safe flag on rails 3, but not
rails 2

test plan:
 * create a quiz with a fill in multiple blanks question
 * preview it
 * it should render the question correctly, not have a bunch
   of raw html

Change-Id: I399874707a880e55c3772e5a780ff595de9062d6
Reviewed-on: https://gerrit.instructure.com/37188
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Ahmad Amireh <ahmad@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>

app/helpers/quizzes_helper.rb

@@ -432,7 +432,8 @@ module QuizzesHelper
       res.gsub! /\{\{question_[^}]+\}\}/, ""
     end
 
-    res
+    # all of our manipulation lost this flag - reset it
+    res.html_safe
   end
 
   def multiple_dropdowns_question(options)

spec/helpers/quizzes_helper_spec.rb

@@ -233,6 +233,7 @@ describe QuizzesHelper do
       )
 
       html.should == %q|<input name="question_1" 'value=&#x27;&gt;&lt;script&gt;alert(&#x27;ha!&#x27;)&lt;/script&gt;&lt;img' readonly="readonly" aria-label='Fill in the blank, read surrounding text' />|
+      html.should be_html_safe
     end
 
     it 'should add an appropriate label' do