Fixed typo in README.md example code

This was the first Ruby gem listed on opencnam.com, so I figured it would just work out of the box and I just blindly copied the code from the README. There was just this tiny pesky bug I had to deal with before (I was hoping) everything would work. :-(

PS: I'm having some other issues though, unfortunately. Going to submit a 2nd pull request.

Best,
Mike