Rename metrics into graph_metrics

[LudovicPatey]

In dramalyzer.py, you define a property called metrics, and then refer to it only as graph_metrics, raising an error. Please, rename metrics into graph_metrics to fix the issue.

[chreman]

Hello, thank you for raising this issue. I haven't had a look at the source code in a long time, can you provide me with a more precise error message?
If this is only a property naming bug and you are confident that the issue is solved by your proposal without side effects I very happily welcome a pull request, as this project is currently not regularly maintained.
Thank you for your understanding!