There should not be any need to edit the plugin to make this work.
Can you please confirm that you have set the settings correctly.
Go to Testimonials > Settings, and click the check-box for Yes next to: Email when a testimonial is submitted?, and add your email address in the field next to: Email address for submission notification.
If these settings are correct, and it is still not working, can you try with a different email address possibly and post back the result.
This feature does work, and has through all of my testing, however it is a new feature and still needs to be thoroughly tested.