Bring back and fix deleted test

It was removed in 755be96 because some tags were allowed, but we can
just update it to check it doesn't remove those tags.

spec/models/budget/phase_spec.rb

@@ -222,4 +222,11 @@ describe Budget::Phase do
     end
   end
 
+  describe "#sanitize_description" do
+    it "removes not allowed html entities from the description" do
+      expect{
+        first_phase.update_attributes(description: '<p><a href="/"><b>a</b></a></p> <script>javascript</script>')
+      }.to change{ first_phase.description }.to('<p><a href="/">a</a></p> javascript')
+    end
+  end
 end