stop using deprecated api in the tests

activerecord/test/cases/fixtures_test.rb

@@ -78,7 +78,7 @@ def test_multiple_clean_fixtures
   end
 
   def test_create_symbol_fixtures
-    fixtures = ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT, :collections, :collections => 'Course') { Course.connection }
+    fixtures = ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT, :collections, :collections => Course) { Course.connection }
 
     assert Course.find_by_name('Collection'), 'course is not in the database'
     assert fixtures.detect { |f| f.name == 'collections' }, "no fixtures named 'collections' in #{fixtures.map(&:name).inspect}"