Restore compatibility with older versions of Node

[SteveSandersonMS]

As of commit d909241 (5 days ago), this package now only runs on Node 4+. Compatibility with Node 0.x was lost because the source code now uses a template literal. Not sure whether that was a deliberate plan or not.

If I sent one, would you accept a simple pull request that restores Node 0.x compatibility?

I know that most people should be on newer versions of Node, but I'd like to take a dependency on to-string-loader in some project templates, and I can't guarantee that everyone runs Node 4+.