Compatibility with Rails LTS 2.3.18.16

[triskweline]

I apologize for making a PR for this very old branch.

We are still maintaining Rails 2.3. A patch CVE-2016-2098 has changed the default render type of render 'template' (it used to be render :file => 'template').

This also breaks the render_template matcher in this gem, which overrides the render method in ActionController to track which template has been rendered.

The attached commit repairs that matcher for recent versions of Rails LTS (1 line changed).

I wonder if you can be bothered to rake release this as a new version 1.3.5?

Again, sorry for this blast from the past.