Cannot spy on inherited class methods

When attempting to spy on inherited class methods, an exception is raise:
```
Failure/Error: spy_on!(TestClass, test_method)
     NameError:
       method `test_method' not defined in Class
```
[Offending line of code](https://github.com/searls/gimme/blob/master/lib/gimme/spies_on_class_methods.rb#L15) is:
`meta_class.send(:remove_method, method)`