Fix HTML entities being parsed in GFM

Also fixes the spec so that it actually tests the thing it says it's
testing. Hooray!

Closes #1308

spec/helpers/gitlab_markdown_helper_spec.rb

@@ -31,6 +31,7 @@ describe GitlabMarkdownHelper do
     end
 
     it "should not touch HTML entities" do
+      @project.issues.stub(:where).with(id: '39').and_return([issue])
       actual = expected = "We'll accept good pull requests."
       gfm(actual).should == expected
     end