Tamsin Gillie

I did notice changing [this line](https://github.com/Katee/aasm-diagram/blob/8419243a7ef6f1eee3c19b364ec1f4dc0f030752/lib/aasm_diagram/diagram.rb#L51) to `@aasm_instance.events` and calling `AASMDiagram::Diagram.new(TestSub.aasm, 'test.png')` does work, but calling `AASMDiagram::Diagram.new(test.aasm, 'test.png')` still does not.

@mihaimuntenas Thank you for the notes! I think the Ruby version I was using did not support the older bundler, but I don't think the upgrade was required after all...

@Katee Is there anything this needs before it can be merged?