Update method_missing exception class

* [1.6](https://github.com/ruby/ruby/blob/e247c4e598dd7807c24173a6c4b92a8dfe0b1caf/eval.c#L4175)
* [1.8.5](https://github.com/ruby/ruby/blob/82ea308dcf767a779c7b3efd930f8d13ea50a5aa/eval.c#L5566)
Merge pull request #27 from kachick/fix-method_missing

Fix method_missing